btrfs: backref: Use ERR_CAST to return error code

Use ERR_CAST() instead of void * to make meaning clear.
Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -2225,7 +2225,7 @@ struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
 
 	fspath = init_data_container(total_bytes);
 	if (IS_ERR(fspath))
-		return (void *)fspath;
+		return ERR_CAST(fspath);
 
 	ifp = kmalloc(sizeof(*ifp), GFP_KERNEL);
 	if (!ifp) {