While clearing the Ports ync mode enable and master select bits
we need to clear the register completely instead of using disable masks

v3:
* Remove reg variable (Matt)
v2:
* Just write 0 to the reg (Ville)
* Rebase

Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/5
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Fixes: 51528afe ("drm/i915/display/icl: Disable transcoder port sync as part of crtc_disable() sequence")
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191228031204.10189-3-manasi.d.navare@intel.com
(cherry picked from commit a3d9382b)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>