Fix Subscriber Add/Delete test - pass olt_id in the flow count check

Change-Id: I87e8e3d6767ebf5a223fa186895ffb8254784839
diff --git a/tests/dt-workflow/Voltha_DT_PODTests.robot b/tests/dt-workflow/Voltha_DT_PODTests.robot
index 9c2d17a..d17f71a 100644
--- a/tests/dt-workflow/Voltha_DT_PODTests.robot
+++ b/tests/dt-workflow/Voltha_DT_PODTests.robot
@@ -127,7 +127,7 @@
         ${onos_flows_count}=    Evaluate    4 * ( ${num_all_onus} - 1 )
         Run Keyword And Continue On Failure    Wait Until Keyword Succeeds    ${timeout}    5s
         ...    Verify Subscriber Access Flows Added Count DT    ${ONOS_SSH_IP}    ${ONOS_SSH_PORT}
-        ...    ${EMPTY}    ${onos_flows_count}
+        ...    ${of_id}    ${onos_flows_count}
         # Verify VOLTHA flows for OLT equals twice the number of ONUS (minus ONU under test) + 1 for LLDP
         ${olt_flows}=    Evaluate    2 * ( ${num_all_onus} - 1 ) + 1
         Run Keyword    Wait Until Keyword Succeeds    ${timeout}    5s    Validate OLT Flows    ${olt_flows}