MAINTAINERS: Include stackleak paths in hardening entry

While most of the gcc-plugins are self-contained in the
scripts/gcc-plugins directory, stackleak actually has some additional
files. Add those so changes are directed to the hardening list.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20231019004616.work.960-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: kees

MAINTAINERS

@@ -8615,6 +8615,8 @@ L:	linux-hardening@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
 F:	Documentation/kbuild/gcc-plugins.rst
+F:	include/linux/stackleak.h
+F:	kernel/stackleak.c
 F:	scripts/Makefile.gcc-plugins
 F:	scripts/gcc-plugins/