selinux: Fix warnings

scripts/selinux/genheaders/genheaders.c:20: warning: no previous prototype
for ?usage?
scripts/selinux/genheaders/genheaders.c:26: warning: no previous prototype
for ?stoupperx?

Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: James Morris <jmorris@namei.org>