Yama: mark function as static

Sparse complains yama_task_prctl can be static. Fix it by making
it static.
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

security/yama/yama_lsm.c

@@ -222,7 +222,7 @@ static void yama_task_free(struct task_struct *task)
  * Return 0 on success, -ve on error.  -ENOSYS is returned when Yama
  * does not handle the given option.
  */
-int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
+static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			   unsigned long arg4, unsigned long arg5)
 {
 	int rc = -ENOSYS;