dm vdo wait-queue: optimize vdo_waitq_dequeue_matching_waiters

Remove temporary 'matched_waiters' waitq and just enqueue matched
waiters directly to the caller provided 'matched_waitq'.

Reviewed-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Matthew Sakai <msakai@redhat.com>