Fix modulated_deform_conv for torch_npu v2.1 (#2941)

Author: 6Vvv

mmcv/ops/modulated_deform_conv.py

@@ -58,7 +58,8 @@ def _npu_forward(ctx, input_tensor, offset, mask, weight, bias):
                 kernel_w, kernel_h, ctx.deform_groups)
         select_offset = offset.index_select(1, sort_index_fp)
         offset_all = torch.cat([select_offset, mask], dim=1)
-        output, offset_out = torch.npu_deformable_conv2d(
+        import torch_npu
+        output, offset_out = torch_npu.npu_deformable_conv2d(
             input_tensor,
             weight,
             offset_all,