optimize workloadspread when suitable subset maxReplicas is niil

Signed-off-by: mingzhou.swx <mingzhou.swx@alibaba-inc.com>

pkg/util/workloadspread/workloadspread.go

@@ -458,6 +458,10 @@ func (h *Handler) updateSubsetForPod(ws *appsv1alpha1.WorkloadSpread,
 				ws.Namespace, ws.Name, pod.Name)
 			return false, nil, ""
 		}
+		// no need to update WorkloadSpread status if MaxReplicas == nil
+		if suitableSubset.MissingReplicas == -1 {
+			return false, suitableSubset, ""
+		}
 		if suitableSubset.CreatingPods == nil {
 			suitableSubset.CreatingPods = map[string]metav1.Time{}
 		}