drm/i915/gt: Add "intel_" as prefix in set_mocs_index()

Adding missing "intel_" prefix in set_mocs_index().

Fixes: b62aa57e ("drm/i915/gt: Add support of mocs propagation")
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Ayaz A Siddiqui <ayaz.siddiqui@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210916062736.1733587-1-ayaz.siddiqui@intel.com