Claude review: drm/xe/ras: Get error threshold support

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

Patch Review

Implements `xe_ras_get_threshold()` which sends a mailbox command to the system controller.

**Issue: No bounds checking on `severity` and `component` parameters before array indexing.**

```c
int xe_ras_get_threshold(struct xe_device *xe, u32 severity, u32 component, u32 *threshold)
{
    ...
    counter.common.severity = drm_to_xe_ras_severities[severity];
    counter.common.component = drm_to_xe_ras_components[component];
```

The `severity` and `component` values come from the drm_ras callback, which passes `error_id` as the component. Although the drm_ras core does range-check `error_id` against `error_counter_range`, there is no explicit bounds check in `xe_ras_get_threshold()` itself against the array sizes of `drm_to_xe_ras_severities[]` and `drm_to_xe_ras_components[]`. Since the caller hard-codes `DRM_XE_RAS_ERR_SEV_CORRECTABLE` for severity, that's safe for now, but the function signature accepts arbitrary `u32` values, making it fragile for future use. At minimum, defensive checks or `BUILD_BUG_ON` assertions tying the array size to expected usage would be prudent.

**Minor: Unused `counter` assignment from response.**

```c
    counter = response.counter;
    *threshold = response.threshold;
```

The `counter` variable is reassigned from the response but only used in the debug print. This is fine for debugging but the local variable `counter` shadows the fact that it was previously the *request* counter — could be confusing. Consider using a separate variable name or just accessing `response.counter.common.*` directly in the debug print.

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