Claude review: drm/v3d: Attach per-fd reset counters to v3d_stats

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

Patch Review

This patch completes the refcounting story by moving the per-fd reset counter into `v3d_stats`. The use of `atomic_t` for both global and per-client reset counters is appropriate since they're now incremented from the reset path without the `reset_lock` held for the per-client counter:

```c
atomic_inc(&v3d->reset_counter);
atomic_inc(&job->client_stats->reset_counter);
```

The `DRM_V3D_PARAM_CONTEXT_RESET_COUNTER` implementation correctly sums across all queues under `reset_lock` to get a consistent snapshot:

```c
mutex_lock(&v3d->reset_lock);
for (enum v3d_queue q = 0; q < V3D_MAX_QUEUES; q++)
    args->value += atomic_read(&v3d_priv->stats[q]->reset_counter);
mutex_unlock(&v3d->reset_lock);
```

The comment explaining why the mutex is still needed here is good.

The removal of the `file_priv` NULL-ing dance in `v3d_postclose` is the culmination of the series and is safe because: (1) `drm_sched_entity_destroy` waits for all entity jobs to complete, so no active job can reference this fd's entity afterward; and (2) the timeout/reset path now uses `job->client_stats` instead of `job->file_priv`.

Note: `DRM_V3D_PARAM_GLOBAL_RESET_COUNTER` no longer takes `reset_lock` since it's a single atomic read. This is correct.

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