Suppress IOU based on box references instead of copying over boxes

This saves us two copies of the entire box class to this call and instead
works on reference of these objects that are created within the loops instead

src/include/migraphx/op/nonmaxsuppression.hpp

@@ -186,7 +186,7 @@ struct nonmaxsuppression
         return result;
     }
 
-    inline bool suppress_by_iou(box b1, box b2, double iou_threshold) const
+    inline bool suppress_by_iou(box& b1, box& b2, double iou_threshold) const
     {
         b1.sort();
         b2.sort();
@@ -290,10 +290,10 @@ struct nonmaxsuppression
                 while(not boxes_heap.empty())
                 {
                     auto iou_candidate_box = boxes_heap.top();
-                    if(not this->suppress_by_iou(
-                           batch_box(batch_boxes_start, iou_candidate_box.second),
-                           next_box,
-                           iou_threshold))
+                    auto iou_candidate     = batch_box(batch_boxes_start, iou_candidate_box.second);
+                    auto suppress_box =
+                        this->suppress_by_iou(iou_candidate, next_box, iou_threshold);
+                    if(not suppress_box)
                     {
                         remainder_boxes.push(iou_candidate_box);
                     }