Fix federated_avg for GPU support + buffers support (#4595)
Fix federated_avg for GPU support + buffers support (#4595)

* Fix federated_avg

* Change copy to deepcopy in federated_avg

Co-authored-by: Kang-Cheng Chen <54298fb077f767bedd387f19b85ba1b5638c58a6@Kang-Chengde-MacBook-Pro.local>
OpenMined/PySyft,OpenMined/PySyft,OpenMined/PySyft,OpenMined/PySyft