Update modeling_qformer.py

Update modeling_qformer to support latest transformers

modeling_qformer.py

@@ -41,6 +41,8 @@ from transformers.modeling_outputs import (
 )
 from transformers.modeling_utils import (
     PreTrainedModel,
+)
+from transformers.pytorch_utils import (
     apply_chunking_to_forward,
     find_pruneable_heads_and_indices,
     prune_linear_layer,