drm/i915/mst: Always write CHICKEN_TRANS

Since we're asked to disable FECSTALL_DIS_DPTSTREAM_DPTTG when
the transcoder is disabled it seems prudent to also clear it
when enabliing the transcoder w/o FEC, just in case
someone else left it enabled by mistake.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231018154123.5479-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>