exec: make prepare_bprm_creds static

prepare_bprm_creds is not used outside exec.c, so there's no reason for it
to have external linkage.

Signed-off-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/exec.c b/fs/exec.c
index fc281b7..b6c9e5f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1399,7 +1399,7 @@ EXPORT_SYMBOL(finalize_exec);
  * Or, if exec fails before, free_bprm() should release ->cred and
  * and unlock.
  */
-int prepare_bprm_creds(struct linux_binprm *bprm)
+static int prepare_bprm_creds(struct linux_binprm *bprm)
 {
 	if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
 		return -ERESTARTNOINTR;