[Bugfix] Fix _synced_weight_loader (#24565)

Signed-off-by: Kyuyeun Kim <kyuyeunk@google.com>

vllm/model_executor/utils.py

@@ -52,10 +52,11 @@ def set_weight_attrs(
 def _make_synced_weight_loader(original_weight_loader):
 
     def _synced_weight_loader(param, *args, **kwargs):
-        original_weight_loader(param, *args, **kwargs)
+        out = original_weight_loader(param, *args, **kwargs)
         # torch._sync doesn't support, is not needed for CPU tensors.
         if param.device != torch.device("cpu"):
             torch._sync(param)
+        return out
 
     return _synced_weight_loader