block: remove q->prepare_flush_fn completely

This removes q->prepare_flush_fn completely (changes the
blk_queue_ordered API).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/drivers/ide/ide-disk.c b/drivers/ide/ide-disk.c
index c22e622..7433e07 100644
--- a/drivers/ide/ide-disk.c
+++ b/drivers/ide/ide-disk.c
@@ -549,7 +549,7 @@
 	} else
 		ordered = QUEUE_ORDERED_DRAIN;
 
-	blk_queue_ordered(drive->queue, ordered, NULL);
+	blk_queue_ordered(drive->queue, ordered);
 }
 
 ide_devset_get_flag(wcache, IDE_DFLAG_WCACHE);