btrfs: don't abuse REQ_OP_* flags for btrfs_map_block

btrfs_map_block supports different types of mappings, which to a large
extent resemble block layer operations.  But they don't always do, and
currently btrfs dangerously overlays it's own flag over the block layer
flags.  This is just asking for a conflict, so introduce a different
map flags enum inside of btrfs instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 75bab76..f7dd892 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -354,8 +354,8 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
 	 * map block
 	 */
 	length = blocksize;
-	ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical, &length,
-			      &bbio, 0);
+	ret = btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS, logical,
+			&length, &bbio, 0);
 	if (ret || !bbio || length < blocksize)
 		goto error;