fix dcn forward bug (#562)

mmcv/ops/csrc/parrots/deform_conv_cuda.cu

@@ -267,6 +267,7 @@ void DeformConvForwardCUDAKernelLauncher(
       auto columns_g = columns[g];
       gemm(ctx, 1, false, weight_g, false, columns_g, 1, output_g);
     }
+    columns = columns.view({columns.dim(0) * columns.dim(1), columns.dim(2)});
   }
 
   output_buffer = output_buffer.view(

mmcv/ops/csrc/pytorch/deform_conv_cuda.cu

@@ -276,6 +276,8 @@ void DeformConvForwardCUDAKernelLauncher(Tensor input, Tensor weight,
                                   .addmm_(weight[g].flatten(1), columns[g])
                                   .view_as(output_buffer[elt][g]);
     }
+    columns =
+        columns.view({columns.size(0) * columns.size(1), columns.size(2)});
   }
 
   output_buffer = output_buffer.view(