QString::sprintf() is deprecated in the latest Qt version, and spawns
a lot of warnings:

  HOSTCXX scripts/kconfig/qconf.o
scripts/kconfig/qconf.cc: In member function ‘void ConfigInfoView::menuInfo()’:
scripts/kconfig/qconf.cc:1090:61: warning: ‘QString& QString::sprintf(const char*, ...)’ is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
 1090 |      head += QString().sprintf("<a href=\"s%s\">", sym->name);
      |                                                             ^
In file included from /usr/include/qt5/QtGui/qkeysequence.h:44,
                 from /usr/include/qt5/QtWidgets/qaction.h:44,
                 from /usr/include/qt5/QtWidgets/QAction:1,
                 from scripts/kconfig/qconf.cc:7:
/usr/include/qt5/QtCore/qstring.h:382:14: note: declared here
  382 |     QString &sprintf(const char *format, ...) Q_ATTRIBUTE_FORMAT_PRINTF(2, 3);
      |              ^~~~~~~
scripts/kconfig/qconf.cc:1099:60: warning: ‘QString& QString::sprintf(const char*, ...)’ is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
 1099 |     head += QString().sprintf("<a href=\"s%s\">", sym->name);
      |                                                            ^
In file included from /usr/include/qt5/QtGui/qkeysequence.h:44,
                 from /usr/include/qt5/QtWidgets/qaction.h:44,
                 from /usr/include/qt5/QtWidgets/QAction:1,
                 from scripts/kconfig/qconf.cc:7:
/usr/include/qt5/QtCore/qstring.h:382:14: note: declared here
  382 |     QString &sprintf(const char *format, ...) Q_ATTRIBUTE_FORMAT_PRINTF(2, 3);
      |              ^~~~~~~
scripts/kconfig/qconf.cc:1127:90: warning: ‘QString& QString::sprintf(const char*, ...)’ is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
 1127 |   debug += QString().sprintf("defined at %s:%d<br><br>", _menu->file->name, _menu->lineno);
      |                                                                                          ^
In file included from /usr/include/qt5/QtGui/qkeysequence.h:44,
                 from /usr/include/qt5/QtWidgets/qaction.h:44,
                 from /usr/include/qt5/QtWidgets/QAction:1,
                 from scripts/kconfig/qconf.cc:7:
/usr/include/qt5/QtCore/qstring.h:382:14: note: declared here
  382 |     QString &sprintf(const char *format, ...) Q_ATTRIBUTE_FORMAT_PRINTF(2, 3);
      |              ^~~~~~~
scripts/kconfig/qconf.cc: In member function ‘QString ConfigInfoView::debug_info(symbol*)’:
scripts/kconfig/qconf.cc:1150:68: warning: ‘QString& QString::sprintf(const char*, ...)’ is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
 1150 |    debug += QString().sprintf("prompt: <a href=\"m%s\">", sym->name);
      |                                                                    ^
In file included from /usr/include/qt5/QtGui/qkeysequence.h:44,
                 from /usr/include/qt5/QtWidgets/qaction.h:44,
                 from /usr/include/qt5/QtWidgets/QAction:1,
                 from scripts/kconfig/qconf.cc:7:
/usr/include/qt5/QtCore/qstring.h:382:14: note: declared here
  382 |     QString &sprintf(const char *format, ...) Q_ATTRIBUTE_FORMAT_PRINTF(2, 3);
      |              ^~~~~~~
scripts/kconfig/qconf.cc: In static member function ‘static void ConfigInfoView::expr_print_help(void*, symbol*, const char*)’:
scripts/kconfig/qconf.cc:1225:59: warning: ‘QString& QString::sprintf(const char*, ...)’ is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
 1225 |   *text += QString().sprintf("<a href=\"s%s\">", sym->name);
      |                                                           ^
In file included from /usr/include/qt5/QtGui/qkeysequence.h:44,
                 from /usr/include/qt5/QtWidgets/qaction.h:44,
                 from /usr/include/qt5/QtWidgets/QAction:1,
                 from scripts/kconfig/qconf.cc:7:
/usr/include/qt5/QtCore/qstring.h:382:14: note: declared here
  382 |     QString &sprintf(const char *format, ...) Q_ATTRIBUTE_FORMAT_PRINTF(2, 3);
      |              ^~~~~~~

The documentation also says:
"Warning: We do not recommend using QString::asprintf() in new Qt code.
Instead, consider using QTextStream or arg(), both of which support
Unicode strings seamlessly and are type-safe."

Use QTextStream as suggested.
Reported-by: Robert Crawford <flacycads@cox.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>