Claude review: drm/display: hdmi-state-helper: Act on color format DRM property

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

Patch Review

Modifies `hdmi_compute_config()` to handle explicit color format requests:

```c
if (conn_state->color_format != DRM_CONNECTOR_COLOR_FORMAT_AUTO) {
	switch (conn_state->color_format) {
	case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
		drm_warn(connector->dev, "AUTO format in non-AUTO path.\n");
		fallthrough;
	case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
		fmt = DRM_OUTPUT_COLOR_FORMAT_RGB444;
		break;
```

The `DRM_CONNECTOR_COLOR_FORMAT_AUTO` case inside the `!= AUTO` guard is deliberately unreachable but exists to satisfy compiler warnings about unhandled enum values. The `drm_warn` + `fallthrough` is a reasonable defensive pattern. Some reviewers might prefer an `unreachable()` or `WARN_ON_ONCE(1)` here instead, but the approach is acceptable.

R-b from Dmitry Baryshkov and Maxime Ripard.

**Verdict**: Good.

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