fix tensorcopy

Author: linjieccc

paddle/pten/kernels/impl/expand_grad_kernel_impl.h

@@ -88,8 +88,7 @@ void ExpandGradKernel(const Context& ctx,
  }
  // no need reduce, just copy
  if (just_copy) {
- ctx.template Alloc<T>(in_grad);
- pten::Copy(ctx, x, false, in_grad);
+ pten::Copy(ctx, out_grad, false, in_grad);
  } else {
  PADDLE_ENFORCE_GE(dims,
  1,