block,fs: use REQ_* flags directly

Remove the WRITE_* and READ_SYNC wrappers, and just use the flags
directly.  Where applicable this also drops usage of the
bio_set_op_attrs wrapper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 147af95..b2abfa4 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1527,7 +1527,7 @@ static struct mapped_device *alloc_dev(int minor)
 
 	bio_init(&md->flush_bio);
 	md->flush_bio.bi_bdev = md->bdev;
-	bio_set_op_attrs(&md->flush_bio, REQ_OP_WRITE, WRITE_FLUSH);
+	md->flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
 
 	dm_stats_init(&md->stats);