fix Wmaybe-uninitialized warning in pooling.cc, test=develop (#28126)
fix Wmaybe-uninitialized warning in pooling.cc, test=develop (#28126)


PaddlePaddle/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,PaddlePaddle/Paddle