use proper variable for resetting associations

kamailio/dispatcher-role.cfg

@@ -121,7 +121,7 @@ route[DISPATCHER_FIND_ROUTES]
         $var(prefered_route) = $sht(associations=>$var(user_source));
         xlog("L_INFO", "$ci|log|found association for contact uri $var(user_source)\n");
         if (!route(DISPATCHER_REORDER_ROUTES)) {
-            $sht(associations=>$var(association)) = $null;
+            $sht(associations=>$var(user_source)) = $null;
         }
     }
 }