dm: fix request-based dm's use of dm_wait_for_completion

The md->wait waitqueue is used by both bio-based and request-based DM.
Commit dbd3bbd291 ("dm rq: leverage blk_mq_queue_busy() to check for
outstanding IO") lost sight of the requirement that
dm_wait_for_completion() must work with all types of DM devices.

Fix md_in_flight() to call the blk-mq or bio-based method accordingly.

Fixes: dbd3bbd291 ("dm rq: leverage blk_mq_queue_busy() to check for outstanding IO")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/dm-rq.c

@@ -131,10 +131,8 @@ static void rq_end_stats(struct mapped_device *md, struct request *orig)
 static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
 {
 	/* nudge anyone waiting on suspend queue */
-	if (unlikely(waitqueue_active(&md->wait))) {
-		if (!blk_mq_queue_busy(md->queue))
-			wake_up(&md->wait);
-	}
+	if (unlikely(waitqueue_active(&md->wait)))
+		wake_up(&md->wait);
 
 	/*
 	 * dm_put() must be at the end of this function. See the comment above