fix roi_pool op bug

paddle/fluid/operators/roi_pool_op.cu

@@ -52,13 +52,19 @@ __global__ void GPUROIPoolForward(
 
     int roi_width = max(roi_end_w - roi_start_w + 1, 1);
     int roi_height = max(roi_end_h - roi_start_h + 1, 1);
-    T bin_size_h = static_cast<T>(roi_height) / static_cast<T>(pooled_height);
-    T bin_size_w = static_cast<T>(roi_width) / static_cast<T>(pooled_width);
 
-    int hstart = static_cast<int>(floor(static_cast<T>(ph) * bin_size_h));
-    int wstart = static_cast<int>(floor(static_cast<T>(pw) * bin_size_w));
-    int hend = static_cast<int>(ceil(static_cast<T>(ph + 1) * bin_size_h));
-    int wend = static_cast<int>(ceil(static_cast<T>(pw + 1) * bin_size_w));
+    int hstart =
+        static_cast<int>(floor(static_cast<T>(ph) * static_cast<T>(roi_height) /
+                               static_cast<T>(pooled_height)));
+    int wstart =
+        static_cast<int>(floor(static_cast<T>(pw) * static_cast<T>(roi_width) /
+                               static_cast<T>(pooled_width)));
+    int hend = static_cast<int>(ceil(static_cast<T>(ph + 1) *
+                                     static_cast<T>(roi_height) /
+                                     static_cast<T>(pooled_height)));
+    int wend = static_cast<int>(ceil(static_cast<T>(pw + 1) *
+                                     static_cast<T>(roi_width) /
+                                     static_cast<T>(pooled_width)));
 
     hstart = min(max(hstart + roi_start_h, 0), height);
     hend = min(max(hend + roi_start_h, 0), height);