drm/i915: use intel_bios_is_port_present()

Don't access i915->vbt.ddi_port_info[] directly.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/42544944ce505826335bab30cc76e135581229be.1579270868.git.jani.nikula@intel.com

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

@@ -265,8 +265,8 @@ void intel_combo_phy_power_up_lanes(struct drm_i915_private *dev_priv,
 
 static u32 ehl_combo_phy_a_mux(struct drm_i915_private *i915, u32 val)
 {
-	bool ddi_a_present = i915->vbt.ddi_port_info[PORT_A].child != NULL;
-	bool ddi_d_present = i915->vbt.ddi_port_info[PORT_D].child != NULL;
+	bool ddi_a_present = intel_bios_is_port_present(i915, PORT_A);
+	bool ddi_d_present = intel_bios_is_port_present(i915, PORT_D);
 	bool dsi_present = intel_bios_is_dsi_present(i915, NULL);
 
 	/*