Update doc for fp16util.py (#50)

update url, original url is not found

modelscope/utils/multi_modal/fp16/fp16util.py

@@ -123,7 +123,7 @@ def prep_param_lists(model, flat_master=False):
         Currently, if ``flat_master=True``, all the model's parameters must be the same type.  If the model has parameters of different types, use ``flat_master=False``, or use :class:`FP16_Optimizer`. # noqa
 
     .. _`Training Neural Networks with Mixed Precision:  Real Examples`:
-        http://on-demand.gputechconf.com/gtc/2018/video/S81012/
+        https://www.nvidia.com/en-us/on-demand/session/gtcsiliconvalley2018-s81012/
     """
     model_params = [
         param for param in model.parameters() if param.requires_grad