drm/i915: Set sync polarity from adjusted mode for TRANS_DP_CTL

Rather than looking at crtc->mode (which is the user mode) dig up the
sync polarity settings from the adjusted_mode when programming
TRANS_DP_CTL on CPT/PPT.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446146763-31821-3-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>