!21126 gird scroll bar示例代码滚动不显示

Merge pull request !21126 from tomkl123/grid_scroll_bar_update

zh-cn/application-dev/reference/arkui-ts/ts-container-grid.md

@@ -187,11 +187,12 @@ struct GridExample {
       .columnsGap(10)
       .rowsGap(10)
       .edgeEffect(EdgeEffect.Spring)
+      .scrollBar(BarState.On)
       .onScrollIndex((first: number) => {
         console.info(first.toString())
       })
       .onScrollBarUpdate((index: number, offset: number) => {
-        return {totalOffset: (index / 5) * (80 + 10) - 10 - offset, totalLength: 80 * 5 + 10 * 4}
+        return {totalOffset: (index / 5) * (80 + 10) - offset, totalLength: 80 * 5 + 10 * 4}
       })
       .width('90%')
       .backgroundColor(0xFAEEE0)