security.h: fix build failure

security.h: fix build failure

include/linux/security.h: In function 'security_ptrace_traceme':
include/linux/security.h:1760: error: 'parent' undeclared (first use in this function)

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: James Morris <jmorris@namei.org>