hurd: Fix st_dev name

[sthibaul]

The real GNU name is st_fsid, but the more commonly known name is st_dev, so better use it to avoid having to fix various rust package.

This also aligns on the existing struct stat field name.

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[JohnTitor]

Thanks! But this crate just provides raw wrappers and changing a name may bring another confusion. I think it's better it remains as-is.

[sthibaul]

@JohnTitor : The current state is way more than confusing: it's not coherent between struct stat and struct stat64.

Long-term wise, keeping this incoherency will be a plague. We'd really much better stick to only the well-known name (which is provided by the C api too).

So far I have not seen a rust software use the st_fsid name, so let's act now to avoid seeing them pop up.

[sthibaul]

So far I have not seen a rust software use the st_fsid name, so let's act now to avoid seeing them pop up.

@JohnTitor : On the other hand, I can quickly see ~45 rust software in debian that use the st_dev field name. Refusing to integrate this PR means imposing us the tedious work to go through all these to introduce an os-specific case, that this PR would avoid altogether. This is imposing us unnecessary work.