futex: Clarify comment for requeue_pi_wake_futex()

 * @hb:		the hash_bucket of the requeue target futex

 *

 * During futex_requeue, with requeue_pi=1, it is possible to acquire the

 * target futex if it is uncontended or via a lock steal.  Set the futex_q key

 * to the requeue target futex so the waiter can detect the wakeup on the right

 * futex, but remove it from the hb and NULL the rt_waiter so it can detect

 * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock

 * to protect access to the pi_state to fixup the owner later.  Must be called

 * with both q->lock_ptr and hb->lock held.

 * target futex if it is uncontended or via a lock steal.

 *

 * 1) Set @q::key to the requeue target futex key so the waiter can detect

 *    the wakeup on the right futex.

 *

 * 2) Dequeue @q from the hash bucket.

 *

 * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock

 *    acquisition.

 *

 * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that

 *    the waiter has to fixup the pi state.

 *

 * 5) Complete the requeue state so the waiter can make progress. After

 *    this point the waiter task can return from the syscall immediately in

 *    case that the pi state does not have to be fixed up.

 *

 * 6) Wake the waiter task.

 *

 * Must be called with both q->lock_ptr and hb->lock held.

 */

static inline

void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,