Fix bug of DCN (#819)

* fix bug of DCN

* fix clang=format

mmcv/ops/csrc/pytorch/deform_conv_cuda.cu

@@ -278,6 +278,8 @@ void DeformConvForwardCUDAKernelLauncher(Tensor input, Tensor weight,
     }
     columns =
         columns.view({columns.size(0) * columns.size(1), columns.size(2)});
+    weight = weight.view({weight.size(0) * weight.size(1), weight.size(2),
+                          weight.size(3), weight.size(4)});
   }
 
   output_buffer = output_buffer.view(