SEBA-468 Use save_changed_fields()

Change-Id: Iff41d3cd5cec9b7211b3b4b644b914e809419f8b
diff --git a/xos/synchronizer/steps/sync_fabric_crossconnect_service_instance.py b/xos/synchronizer/steps/sync_fabric_crossconnect_service_instance.py
index 0880988..2481af8 100644
--- a/xos/synchronizer/steps/sync_fabric_crossconnect_service_instance.py
+++ b/xos/synchronizer/steps/sync_fabric_crossconnect_service_instance.py
@@ -142,7 +142,7 @@
         #   to detect someone changing those.
 
         o.backend_handle = self.make_handle(o.s_tag, o.switch_datapath_id)
-        o.save(update_fields=["backend_handle"])
+        o.save_changed_fields()
 
         self.log.info("ONOS response", res=r.text)