drm/i915/dp: Fix DSC enable code to use cpu_transcoder instead of encoder->type

drm/i915/dp: Fix DSC enable code to use cpu_transcoder instead of encoder->type

This patch fixes the intel_configure_pps_for_dsc_encoder() function to use
cpu_transcoder instead of encoder->type to select the correct DSC registers
that was wrongly used in the original patch for one DSC register isntance.

Fixes: 7182414e2530 ("drm/i915/dp: Configure i915 Picture parameter Set registers during DSC enabling")
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.0+
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190821215950.24223-1-manasi.d.navare@intel.com
(cherry picked from commit d4c61c4a16decd8ace8660f22c81609a539fccba)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>