SEBA-612 Port SEBA-571 changes to tt-workflow-driver

Change-Id: I8d6933805fa0106979e9f2e4bd6ac68be0f51e6c
diff --git a/xos/synchronizer/helpers.py b/xos/synchronizer/helpers.py
index a300892..efdce1a 100644
--- a/xos/synchronizer/helpers.py
+++ b/xos/synchronizer/helpers.py
@@ -40,7 +40,8 @@
 
         whitelisted = matching_entries[0]
         try:
-            pon_port = model_accessor.ONUDevice.objects.get(serial_number=tt_si.serial_number).pon_port
+            onu = model_accessor.ONUDevice.objects.get(serial_number=tt_si.serial_number)
+            pon_port = onu.pon_port
         except IndexError:
             raise DeferredException("ONU device %s is not know to XOS yet" % tt_si.serial_number)