Return list of nodeids

No need to return parameters, only contains list of nodeids.

asyncua/client/ua_client.py

@@ -611,7 +611,7 @@ class UaClient:
         response = struct_from_binary(ua.RegisterNodesResponse, data)
         self.logger.debug(response)
         response.ResponseHeader.ServiceResult.check()
-        return response.Parameters
+        return response.Parameters.RegisteredNodeIds
 
     def unregister_nodes(self, nodes):
         self.logger.info("unregister_nodes")