scoutfs: init ret when freeing zero extents

The server forgot to initialize ret to 0 and might return
undefined errnos if a client asked it to free zero extents.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/server.c

@@ -746,7 +746,7 @@ static int server_free_extents(struct super_block *sb,
 	DECLARE_SERVER_INFO(sb, server);
 	struct scoutfs_net_extent_list *nexl;
 	struct commit_waiter cw;
-	int ret;
+	int ret = 0;
 	int err;
 	u64 i;