btrfs: add free space tree to the cow-only list

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -575,7 +575,8 @@ static int is_cowonly_root(u64 root_objectid)
 	    root_objectid == BTRFS_TREE_LOG_OBJECTID ||
 	    root_objectid == BTRFS_CSUM_TREE_OBJECTID ||
 	    root_objectid == BTRFS_UUID_TREE_OBJECTID ||
-	    root_objectid == BTRFS_QUOTA_TREE_OBJECTID)
+	    root_objectid == BTRFS_QUOTA_TREE_OBJECTID ||
+	    root_objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
 		return 1;
 	return 0;
 }