fix cuda error 700 for softmax (#74298)

Author: fxyfxy777

paddle/phi/kernels/gpudnn/softmax_gpudnn.h

@@ -1375,7 +1375,7 @@ void SoftmaxBackwardCUDAKernelDriverImpl(const GPUContext& dev_ctx,
  GetSoftmaxTensorDims<IndexType>(out.dims(), axis);
  IndexType N = tensor_dims[0];
  IndexType dim = tensor_dims[1];
- int D = tensor_dims[2];
+ IndexType D = tensor_dims[2];
 
  if (D == 1) {
  if (!UseCudnnSoftmax<T>(dev_ctx, dim, true) ||