Fix: [CAN][STM32] GCC compile errors.

[GibbyChan]

拉取/合并请求描述：(PR description)

[

为什么提交这份PR (why to submit this PR)

gcc 编译错误
compile error with gcc

你的解决方案是什么 (what is your solution)

错误原因在于标签后使用声明，因此在新的作用域中声明变量。
Error is caused by using a declaration after a label; therefore, declare the variable within a new scope.

请提供验证的bsp和config (provide the config and bsp)

• BSP: STM32F103

• .config:

• action:

]

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了
As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比
  Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格
  Style guide is adhered to, including spacing, naming and
  other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已
  经被注释了的代码
  All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件
  代码或BSP
  All modifications are justified and not affect other
  components or BSP
• 对难懂代码均提供对应的注释
  I've commented appropriately where code is tricky
• 代码是高质量的
  Code in this PR is of high quality
• 已经使用formatting 等源码格式化工具确保格式符合RT-Thread代码规范
  This PR complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/workflows/bsp_buildings.yml 详细请参考链接BSP自查

[CLAassistant]

All committers have signed the CLA.