dm: remove unnecessary wrapper around blk_lld_busy

There is no need for DM to export a wrapper around the already exported
blk_lld_busy().

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1627,7 +1627,7 @@ static int __pgpath_busy(struct pgpath *pgpath)
 {
 	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
 
-	return dm_underlying_device_busy(q);
+	return blk_lld_busy(q);
 }
 
 /*