Bugfix for bmm style expert nvfp4 weight scale export (#384)

Signed-off-by: Zhiyu Cheng <[email protected]>

Author: Edwardf0t1

modelopt/torch/export/unified_export_hf.py

@@ -332,6 +332,10 @@ def _export_quantized_weight(
 
     setattr(sub_module, weight_name, nn.Parameter(quantized_weight, requires_grad=False))
 
+    # Register the corrected weight_scale as a buffer
+    if weight_scale is not None:
+        sub_module.register_buffer(quantizer_attrs.weight_scale, weight_scale)
+
 
 def _export_hf_checkpoint(
     model: nn.Module, dtype: torch.dtype | None = None