drm/i915/display: replace IS_GEN() in commented code

Since we are replacing IS_GEN() with GRAPHICS_VER(), make sure we take
care of the comments as well.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603165428.3625495-8-lucas.demarchi@intel.com

drivers/gpu/drm/i915/display/intel_tv.c

@@ -1307,7 +1307,7 @@ intel_tv_compute_config(struct intel_encoder *encoder,
 	 * the active portion. Hence following this formula seems
 	 * more trouble that it's worth.
 	 *
-	 * if (IS_GEN(dev_priv, 4)) {
+	 * if (GRAPHICS_VER(dev_priv) == 4) {
 	 *	num = cdclk * (tv_mode->oversample >> !tv_mode->progressive);
 	 *	den = tv_mode->clock;
 	 * } else {