Fixes port update failure when device ID is not updated

The updation was failing because the changed_device_id variable
was undeclared.This fix declares the variable with a default value
at the beginning of the method.

Change-Id: I06dfea1170a6b2a649f4e1efe4bf70b7cee0eacb
Closes-Bug: 1337787
Merge "Fixes port update failure when device ID is not updated"