Use defer style to stop tickers to avoid current/possible misuse (#5883)

This commit ensures that all tickers are stopped using defer ticker.Stop()
style. This will also fix one bug seen when a client starts to listen to
event notifications and that case will result a leak in tickers.

cmd/xl-v1-multipart.go

@@ -837,11 +837,11 @@ func (xl xlObjects) AbortMultipartUpload(ctx context.Context, bucket, object, up
 // Clean-up the old multipart uploads. Should be run in a Go routine.
 func (xl xlObjects) cleanupStaleMultipartUploads(ctx context.Context, cleanupInterval, expiry time.Duration, doneCh chan struct{}) {
 	ticker := time.NewTicker(cleanupInterval)
+	defer ticker.Stop()
 
 	for {
 		select {
 		case <-doneCh:
-			ticker.Stop()
 			return
 		case <-ticker.C:
 			var disk StorageAPI