kernel: doc: remove outdated comment cred.c

This removes an outdated comment in prepare_kernel_cred.

There is no "cred_replace_mutex" any more, so the comment must
go away.
Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

kernel/cred.c

@@ -675,8 +675,6 @@ void __init cred_init(void)
  * The caller may change these controls afterwards if desired.
  *
  * Returns the new credentials or NULL if out of memory.
- *
- * Does not take, and does not return holding current->cred_replace_mutex.
  */
 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 {