Fix run.py for new op.model

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

benchmark/run.py

@@ -134,7 +134,7 @@ elif args.format == 'onnx':
         for o_n in output_names:
             dynamic_axes[o_n] = {0: 'batch_size', 1: 'sequence_length'}
         torch.onnx.export(
-            op.model,
+            op.model.model,
             tuple(inputs.values()),
             onnx_path,
             input_names=input_names,