Fix some bugs for two stage training of deformable detr (#25045)

* Update modeling_deformable_detr.py

Fix bugs for two stage training

* Update modeling_deformable_detr.py

* Add test_two_stage_training to DeformableDetrModelTest

---------

Co-authored-by: yupeng.jia <yupeng.jia@momenta.ai>

tests/models/deformable_detr/test_modeling_deformable_detr.py

@@ -544,6 +544,21 @@ class DeformableDetrModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineT
                         msg=f"Parameter {name} of model {model_class} seems not properly initialized",
                     )
 
+    def test_two_stage_training(self):
+        model_class = DeformableDetrForObjectDetection
+        config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()
+        config.return_dict = True
+        config.two_stage = True
+        config.auxiliary_loss = True
+        config.with_box_refine = True
+
+        model = model_class(config)
+        model.to(torch_device)
+        model.train()
+        inputs = self._prepare_for_class(inputs_dict, model_class, return_labels=True)
+        loss = model(**inputs).loss
+        loss.backward()
+
 
 TOLERANCE = 1e-4