Claude review: rust: devres: return reference in `devres::register`

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This patch changes `devres::register` from returning `Result` to `Result<&'a T>`, tying the lifetime of the returned reference to the `&'a Device<Bound>` argument.

**The lifetime reasoning is sound.** As long as you hold `&Device<Bound>`, the device is bound and devres-managed data won't be freed, so the pointer remains valid for `'a`.

The raw pointer capture before the move is the right approach:
```rust
let data_ptr = &raw const *data;

register_foreign(dev, data)
    .map(|()| unsafe { &*data_ptr })
```

**Callers updated correctly.** Both `cpufreq.rs` and `drm/driver.rs` now use `?;` + `Ok(())` since they don't need the returned reference — they just discard it. This is a clean, backward-compatible change.

No issues with this patch.

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