[Fix] Add missing contiguous calls for nms_rotated (open-mmlab#2547)

Addresses issue open-mmlab#2542

For nms_rotated_cuda only adds contiguous call to dets_sorted which is accessed directly.
For nms_rotated_cpu the implementation now matches what's in the detectron2 repo.

mmcv/ops/csrc/pytorch/nms_rotated.cpp

@@ -26,8 +26,8 @@ Tensor nms_rotated(const Tensor dets, const Tensor scores, const Tensor order,
   assert(dets.device().is_cuda() == scores.device().is_cuda());
   if (dets.device().is_cuda()) {
 #ifdef MMCV_WITH_CUDA
-    return nms_rotated_cuda(dets, scores, order, dets_sorted, iou_threshold,
-                            multi_label);
+    return nms_rotated_cuda(dets, scores, order, dets_sorted.contiguous(),
+                            iou_threshold, multi_label);
 #else
     AT_ERROR("Not compiled with GPU support");
 #endif
@@ -39,5 +39,5 @@ Tensor nms_rotated(const Tensor dets, const Tensor scores, const Tensor order,
 #endif
   }
 
-  return nms_rotated_cpu(dets, scores, iou_threshold);
+  return nms_rotated_cpu(dets.contiguous(), scores.contiguous(), iou_threshold);
 }