User namespaces: use the current_user_ns() macro

Fix up the last current_user()->user_ns instance to use
current_user_ns().

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>

kernel/user.c

@@ -361,7 +361,7 @@ struct user_struct *find_user(uid_t uid)
 {
 	struct user_struct *ret;
 	unsigned long flags;
-	struct user_namespace *ns = current_user()->user_ns;
+	struct user_namespace *ns = current_user_ns();
 
 	spin_lock_irqsave(&uidhash_lock, flags);
 	ret = uid_hash_find(uid, uidhashentry(ns, uid));