Fix UltimateTTT::MaxGameLength

The max game length of an ultimate TTT relies on the max length
of its meta TTT game. Encapsulate this instead of re-implementing
TicTacToe::MaxGameLenth in UltimateTTT::MaxGameLenth.

Signed-off-by: odanrc <odanrc@yahoo.com.br>

open_spiel/games/ultimate_tic_tac_toe/ultimate_tic_tac_toe.h

@@ -93,7 +93,7 @@ class UltimateTTTGame : public Game {
             tic_tac_toe::kNumRows, tic_tac_toe::kNumCols};
   }
   int MaxGameLength() const override {
-    return tic_tac_toe::kNumCells * kNumSubgames;
+    return ttt_game_->MaxGameLength() * kNumSubgames;
   }
 
   const tic_tac_toe::TicTacToeGame* TicTacToeGame() const {