stack_msg in upstream code is only used in securit/apparmor/domain.c
so declare it as static.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311092251.TwKSNZ0u-lkp@intel.com/Signed-off-by: John Johansen <john.johansen@canonical.com>