kernel/user.c: add lock release annotation on free_user()

free_user() releases uidhash_lock but was missing annotation.  Add it.
This removes following sparse warnings:

 include/linux/spinlock.h:339:9: warning: context imbalance in 'free_user' - unexpected unlock
 kernel/user.c:120:6: warning: context imbalance in 'free_uid' - wrong count at exit
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dhaval Giani <dhaval.giani@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/user.c

@@ -91,6 +91,7 @@ static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
  * upon function exit.
  */
 static void free_user(struct user_struct *up, unsigned long flags)
+	__releases(&uidhash_lock)
 {
 	uid_hash_remove(up);
 	spin_unlock_irqrestore(&uidhash_lock, flags);