dm mpath: fix lock order inconsistency in multipath_ioctl

Commit 3e9f1be1b40 ("dm mpath: remove process_queued_ios()") did not
consistently take the multipath device's spinlock (m->lock) before
calling dm_table_run_md_queue_async() -- which takes the q->queue_lock.

Found with code inspection using hint from reported lockdep warning.

Reported-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1566,8 +1566,8 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
 		}
 		if (m->pg_init_required)
 			__pg_init_all_paths(m);
-		spin_unlock_irqrestore(&m->lock, flags);
 		dm_table_run_md_queue_async(m->ti->table);
+		spin_unlock_irqrestore(&m->lock, flags);
 	}
 
 	return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);