fix win compile error: EigenTenor * float unsupport. test=develop

paddle/fluid/operators/grid_sampler_op.h

@@ -63,12 +63,19 @@ static void CalcGridLocations(const platform::CPUDeviceContext& ctx,
   Tensor ones;
   ones.mutable_data<T>({n, h, w}, ctx.GetPlace());
   auto ones_t = EigenTensor<T, 3>::From(ones).setConstant(1.0);
+  Tensor half_xmax, half_ymax;
+  half_xmax.mutable_data<T>({n, h, w}, ctx.GetPlace());
+  auto half_xmax_t =
+      EigenTensor<T, 3>::From(half_xmax).setConstant(0.5 * x_max);
+  half_ymax.mutable_data<T>({n, h, w}, ctx.GetPlace());
+  auto half_ymax_t =
+      EigenTensor<T, 3>::From(half_ymax).setConstant(0.5 * y_max);
 
   // scale grid to [0, h-1/w-1]
   auto grid_x_t = EigenTensor<T, 3>::From(grid_x);
   auto grid_y_t = EigenTensor<T, 3>::From(grid_y);
-  grid_x_t.device(place) = 0.5 * ((grid_x_t + ones_t) * x_max);
-  grid_y_t.device(place) = 0.5 * ((grid_y_t + ones_t) * y_max);
+  grid_x_t.device(place) = (grid_x_t + ones_t) * half_xmax_t;
+  grid_y_t.device(place) = (grid_y_t + ones_t) * half_ymax_t;
 
   // calculate coords of 4 corner points
   x_w->mutable_data<T>({n, h, w}, ctx.GetPlace());