lib/vsprintf: Add a note on re-using %pf or %pF

Add a note warning of re-use of obsolete %pf or %pF extensions.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

lib/vsprintf.c

@@ -2017,6 +2017,8 @@ static char *kobject_string(char *buf, char *end, void *ptr,
  * - 'S' For symbolic direct pointers (or function descriptors) with offset
  * - 's' For symbolic direct pointers (or function descriptors) without offset
  * - '[Ss]R' as above with __builtin_extract_return_addr() translation
+ * - '[Ff]' %pf and %pF were obsoleted and later removed in favor of
+ *	    %ps and %pS. Be careful when re-using these specifiers.
  * - 'B' For backtraced symbolic direct pointers with offset
  * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
  * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]