drm/i915: Add missing doc for drm_i915_reset_stats

Add missing doc for struct drm_i915_reset_stats.

Cc: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240229132918.10205-1-nirmoy.das@intel.com