drm/i915: Replace aux_ch_ctl_reg check with port check

Instead of checking what aux_ch_ctl_reg is, we can simply check the port
when determining the right timeout value to program.

v2: Reorder patches to reduce churn (Chris)
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Link: http://patchwork.freedesktop.org/patch/msgid/1447266856-30249-2-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -750,7 +750,7 @@ static uint32_t i9xx_get_aux_send_ctl(struct intel_dp *intel_dp,
 	else
 		precharge = 5;
 
-	if (IS_BROADWELL(dev) && intel_dp->aux_ch_ctl_reg == DPA_AUX_CH_CTL)
+	if (IS_BROADWELL(dev) && intel_dig_port->port == PORT_A)
 		timeout = DP_AUX_CH_CTL_TIME_OUT_600us;
 	else
 		timeout = DP_AUX_CH_CTL_TIME_OUT_400us;