futex: Use futex_top_waiter() in lookup_pi_state()

lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,

		union futex_key *key, struct futex_pi_state **ps)

{

	struct futex_q *match = futex_top_waiter(hb, key);

	struct futex_pi_state *pi_state = NULL;

	struct futex_q *this, *next;

	struct task_struct *p;

	pid_t pid = uval & FUTEX_TID_MASK;

	plist_for_each_entry_safe(this, next, &hb->chain, list) {

		if (match_futex(&this->key, key)) {

	if (match) {

		/*

			 * Sanity check the waiter before increasing

			 * the refcount and attaching to it.

		 * Sanity check the waiter before increasing the

		 * refcount and attaching to it.

		 */

			pi_state = this->pi_state;

		pi_state = match->pi_state;

		/*

			 * Userspace might have messed up non-PI and

			 * PI futexes [3]

		 * Userspace might have messed up non-PI and PI

		 * futexes [3]

		 */

		if (unlikely(!pi_state))

			return -EINVAL;

		*ps = pi_state;

		return 0;

	}

	}

	/*

	 * We are the first waiter - try to look up the real owner and attach