block/loop: queue ordered mode should be DRAIN_FLUSH

loop implements FLUSH using fsync but was incorrectly setting its
ordered mode to DRAIN.  Change it to DRAIN_FLUSH.  In practice, this
doesn't change anything as loop doesn't make use of the block layer
ordered implementation.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

drivers/block/loop.c

@@ -832,7 +832,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	lo->lo_queue->unplug_fn = loop_unplug;
 
 	if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
-		blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN);
+		blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN_FLUSH);
 
 	set_capacity(lo->lo_disk, size);
 	bd_set_size(bdev, size << 9);