Btrfs: avoid positive number with ERR_PTR

inode_ref_info() returns 1 when the element wasn't found and < 0 on error,
just like btrfs_search_slot(). In iref_to_path() it's an error when the
inode ref can't be found, thus we return ERR_PTR(ret) in that case. In order
to avoid ERR_PTR(1), we now set ret to -ENOENT in that case.
Signed-off-by: NJan Schmidt <list.btrfs@jan-o-sch.net>

fs/btrfs/backref.c

@@ -892,6 +892,8 @@ static char *iref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
 		if (eb != eb_in)
 			free_extent_buffer(eb);
 		ret = inode_ref_info(parent, 0, fs_root, path, &found_key);
+		if (ret > 0)
+			ret = -ENOENT;
 		if (ret)
 			break;
 		next_inum = found_key.offset;