return actual error if failing to update alert data

(cherry picked from commit 36aec52c08)

pkg/services/dashboards/dashboard_service.go

@@ -165,7 +165,7 @@ func (dr *dashboardServiceImpl) updateAlerting(cmd *models.SaveDashboardCommand,
 	}
 
 	if err := bus.Dispatch(&alertCmd); err != nil {
-		return models.ErrDashboardFailedToUpdateAlertData
+		return err
 	}
 
 	return nil