fix rotated bounding box tracing inference error

Summary:
Pull Request resolved: #4249

Fixes run time error:
RuntimeError: Output 0 of SelectBackward0 is a view and is being modified inplace. This view is the output of a function that returns multiple views. Such functions do not allow the output views to be modified inplace. You should replace the inplace operation by an out-of-place one.

Reviewed By: zhanghang1989

Differential Revision: D36433376

fbshipit-source-id: e337e63e2ce09632d42db79a7b6e7b050ceb325c

Author: sstsai-adl

detectron2/modeling/roi_heads/rotated_fast_rcnn.py

@@ -80,6 +80,7 @@ def fast_rcnn_inference_rotated(
     return [x[0] for x in result_per_image], [x[1] for x in result_per_image]
 
 
+@torch.no_grad()
 def fast_rcnn_inference_single_image_rotated(
     boxes, scores, image_shape, score_thresh, nms_thresh, topk_per_image
 ):