Claude review: drm: Define a conditional guard for drm_dev_{enter,exit}()

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

Patch Review

```c
DEFINE_LOCK_GUARD_1(drm_dev, struct drm_device,
        { WARN_ON("Use cond guards"); _T->idx = -1; },
        drm_dev_exit(_T->idx), int idx);
DEFINE_LOCK_GUARD_1_COND(drm_dev, _access, drm_dev_enter(_T->lock, &_T->idx));
```

The base `drm_dev` guard intentionally WARNs if used directly (since `drm_dev_enter` can fail, it only makes sense as a conditional guard). The string `"Use cond guards"` in `WARN_ON()` is a non-zero pointer which will always evaluate to true — this means any unconditional `guard(drm_dev)` will always WARN. This is the intended design. However, it would be slightly cleaner to use `WARN_ON(true)` or `WARN_ON_ONCE(1)` with a comment, since passing a string to `WARN_ON` is unusual and might confuse readers. Minor style nit.

This also touches shared DRM infrastructure (drm_drv.h) and needs broader acks.

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Generated by Claude Code Patch Reviewer