Btrfs: Fix variable init during csum creation

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/file-item.c

@@ -325,6 +325,7 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
 	item = btrfs_lookup_csum(trans, root, path, objectid, offset, 1);
 	if (!IS_ERR(item)) {
 		leaf = path->nodes[0];
+		ret = 0;
 		goto found;
 	}
 	ret = PTR_ERR(item);