scripts/kallsyms: update the usage in the comment block

Commit 010a0aad ("kallsyms: Correctly sequence symbols when
CONFIG_LTO_CLANG=y") added --lto-clang, and updated the usage()
function, but not the comment. Update it in the same way.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/kallsyms.c

@@ -6,7 +6,7 @@
  * of the GNU General Public License, incorporated herein by reference.
  *
  * Usage: kallsyms [--all-symbols] [--absolute-percpu]
- *                         [--base-relative] in.map > out.S
+ *                         [--base-relative] [--lto-clang] in.map > out.S
  *
  *      Table compression uses all the unused char codes on the symbols and
  *  maps these to the most used substrings (tokens). For instance, it might