[Fix] Fix modulated_deform_conv.py for torch_npu v2.1 (#2983)

Author: shun001

mmcv/ops/modulated_deform_conv.py

@@ -83,8 +83,9 @@ def _npu_forward(ctx, input_tensor, offset, mask, weight, bias):
     def _npu_backward(ctx, grad_output):
         input_tensor, weight, offset_out, offset_all, sort_index_bp = \
             ctx.saved_tensors
+        import torch_npu
         grad_input, grad_weight, grad_offset_all, grad_bias = \
-            torch.npu_deformable_conv2dbk(
+            torch_npu.npu_deformable_conv2dbk(
                 input_tensor, grad_output, offset_out, weight, offset_all,
                 kernel_size=[weight.shape[3], weight.shape[2]],
                 stride=[1, 1, ctx.stride[0], ctx.stride[1]],