Use torch.device instead of current device index for BnB quantizer (#10069)

* update

* apply review suggestion

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

src/diffusers/models/model_loading_utils.py

@@ -176,6 +176,8 @@ def load_model_dict_into_meta(
     hf_quantizer=None,
     keep_in_fp32_modules=None,
 ) -> List[str]:
+    if device is not None and not isinstance(device, (str, torch.device)):
+        raise ValueError(f"Expected device to have type `str` or `torch.device`, but got {type(device)=}.")
     if hf_quantizer is None:
         device = device or torch.device("cpu")
     dtype = dtype or torch.float32

src/diffusers/models/modeling_utils.py

@@ -836,7 +836,7 @@ class ModelMixin(torch.nn.Module, PushToHubMixin):
                         param_device = "cpu"
                     # TODO (sayakpaul,  SunMarc): remove this after model loading refactor
                     elif is_quant_method_bnb:
-                        param_device = torch.cuda.current_device()
+                        param_device = torch.device(torch.cuda.current_device())
                     state_dict = load_state_dict(model_file, variant=variant)
                     model._convert_deprecated_attention_blocks(state_dict)