drm/i915: Don't propagate the gen split confusion further

There's no such thing as gen13. It is either display 13
or graphics 13. Don't propagate the gen12 confusion
further.

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015091650.87270-1-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -8263,7 +8263,7 @@ enum {
 
 /*
  * The below are numbered starting from "S1" on gen11/gen12, but starting
- * with gen13 display, the bspec switches to a 0-based numbering scheme
+ * with display 13, the bspec switches to a 0-based numbering scheme
  * (although the addresses stay the same so new S0 = old S1, new S1 = old S2).
  * We'll just use the 0-based numbering here for all platforms since it's the
  * way things will be named by the hardware team going forward, plus it's more