vvp: Fix time scaling when using vpiScaledRealTime in VPI callbacks.

The old code only worked for VPI objects that represented variables
and nets. For simulation time callbacks, the user might pass an
object that represents a scope.

vvp/vpi_callback.cc

@@ -51,9 +51,7 @@ static void set_callback_time(p_cb_data data)
 	    vpip_time_to_timestruct(data->time, schedule_simtime());
 	    break;
 	  case vpiScaledRealTime:
-	    data->time->real =
-	         vpip_time_to_scaled_real(schedule_simtime(),
-	             data->obj ? static_cast<__vpiScope *>(vpi_handle(vpiScope, data->obj)) : 0);
+	    data->time->real = vpip_scaled_time_from_handle(schedule_simtime(), data->obj);
 	    break;
 	  case vpiSuppressTime:
 	    break;