drm/i915: Use intel_ddi_dp_voltage_max() for HSW/BDW too

Use intel_ddi_dp_voltage_max() for HSW/BDW too instead of letting these
fall through the if ladder in a weird way. This function will look at
the actual buf trans tables we have for HSW/BDW to determine the max
vswing level.

It looks to me like the current code leads HSW port A down the IVB port
A path, HSW port B+ and BDW fall through to the very end. Both cases do
result in the correct max vswing level 2, but it's very hard to see that
from the code.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180517170309.28630-1-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -3220,12 +3220,12 @@ uint8_t
 intel_dp_voltage_max(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *dev_priv = to_i915(intel_dp_to_dev(intel_dp));
-	enum port port = dp_to_dig_port(intel_dp)->base.port;
+	struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+	enum port port = encoder->port;
 
-	if (INTEL_GEN(dev_priv) >= 9) {
-		struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+	if (HAS_DDI(dev_priv))
 		return intel_ddi_dp_voltage_max(encoder);
-	} else if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
+	else if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 	else if (IS_GEN7(dev_priv) && port == PORT_A)
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;