simplify returning boolean expression in staging/src/k8s.io/client-go/tools

Signed-off-by: 刁浩 10284789 <diao.hao@zte.com.cn>

Kubernetes-commit: 9173414da6d1c70436b256d6068e3737a7434f6a

tools/cache/fifo.go

@@ -263,10 +263,7 @@ func (f *FIFO) GetByKey(key string) (item interface{}, exists bool, err error) {
 func (f *FIFO) IsClosed() bool {
 	f.lock.Lock()
 	defer f.lock.Unlock()
-	if f.closed {
-		return true
-	}
-	return false
+	return f.closed
 }
 
 // Pop waits until an item is ready and processes it. If multiple items are