drm/i915/gt: add sparse lock annotation to avoid warnings

Annotate intel_gt_mcr_lock() and intel_gt_mcr_unlock() to fix sparse
warnings:

drivers/gpu/drm/i915/gt/intel_gt_mcr.c:397:9: warning: context imbalance in 'intel_gt_mcr_lock' - wrong count at exit
drivers/gpu/drm/i915/gt/intel_gt_mcr.c:412:6: warning: context imbalance in 'intel_gt_mcr_unlock' - unexpected unlock

Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230207124026.2105442-1-jani.nikula@intel.com