[kernel]: Fix/blk gnu conditional extension

[rsj123]

拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

components/drivers/block/blk.c 第549行和第564行使用了 GNU C 扩展语法 ? :，省略了中间操作数，该语法在 IAR 编译器中不支持。
#10385

你的解决方案是什么 (what is your solution)

使用临时变量 mnt_path 保存 dfs_filesystem_get_mounted_path() 的返回值，将 GNU 扩展 ? : 替换为标准 C 三元运算符 expr ? expr : default。

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

• BSP:

• .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/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
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  Set files/directories to exclude (directories should end with "/")
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Once completed, commits will be pushed to the fix/blk-gnu-conditional-extension branch automatically, and the related Pull Request will be updated.

如有问题欢迎联系我们，再次感谢您的贡献！💐
If you have any questions, feel free to reach out. Thanks again for your contribution!

[github-actions]

📌 Code Review Assignment

🏷️ Tag: components

Reviewers: Maihuanyi

Changed Files (Click to expand)

• components/drivers/block/blk.c

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📊 Current Review Status (Last Updated: 2026-02-21 13:23 CST)

• ⌛ Maihuanyi Pending Review

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📝 Review Instructions

1. 维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
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   Comment LGTM/lgtm after confirming approval

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