[drivers][dac] Fix wrong rt_dac_write arguments in doxygen example

[mnikapl954]

拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

The doxygen example in dac.h calls rt_dac_write with four arguments and passes DAC_DEV_NAME as the second parameter. The public API only accepts three parameters (dev, channel, value), so the example does not compile and misleads users (same class of error as discussed in #6568).

你的解决方案是什么 (what is your solution)

Update the example to:

c rt_dac_write(dac_dev, DAC_DEV_CHANNEL, value);

Change is limited to the doxygen Example block in components/drivers/include/drivers/dac.h.

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

• BSP: N/A (documentation / doxygen example only)
• Validation: compared example against rt_dac_write prototype and the MSH helper in components/drivers/misc/dac.c

当前拉取/合并请求的状态 Intent for your PR

• 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：

• 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 Style guide is adhered to
• 没有垃圾代码 All redundant code is removed
• 所有变更均有原因及合理的 All modifications are justified
• 代码是高质量的 Code in this PR is of high quality

[github-actions]

📌 Code Review Assignment

🏷️ Tag: components

Reviewers: @Maihuanyi

Changed Files (Click to expand)

• components/drivers/include/drivers/dac.h

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📊 Current Review Status (Last Updated: 2026-07-22 16:38 CST)

• ⌛ @Maihuanyi Pending Review

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[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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