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/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 09ed29c..f137ffe 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -62,7 +62,7 @@ struct btrfs_device {
 	int running_pending;
 	/* regular prio bios */
 	struct btrfs_pending_bios pending_bios;
-	/* WRITE_SYNC bios */
+	/* sync bios */
 	struct btrfs_pending_bios pending_sync_bios;
 
 	struct block_device *bdev;