drm/i915: Correct ss -> steering calculation for pre-Xe_HP platforms

Accidental use of a "SLICE" macro where a "SUBSLICE" macro was intended
causes the group ID for steering to be calculated incorrectly on
pre-Xe_HP platforms.

Fixes: 9a92732 ("drm/i915/gt: Add general DSS steering iterator to intel_gt_mcr")
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220712220513.3451794-1-matthew.d.roper@intel.com

drivers/gpu/drm/i915/gt/intel_gt_mcr.c

@@ -515,7 +515,7 @@ void intel_gt_mcr_get_ss_steering(struct intel_gt *gt, unsigned int dss,
 		*group = dss / GEN_DSS_PER_GSLICE;
 		*instance = dss % GEN_DSS_PER_GSLICE;
 	} else {
-		*group = dss / GEN_MAX_HSW_SLICES;
+		*group = dss / GEN_MAX_SS_PER_HSW_SLICE;
 		*instance = dss % GEN_MAX_SS_PER_HSW_SLICE;
 		return;
 	}