For an enabled DSC during HW readout the corresponding power reference
is taken along the CRTC power domain references in
get_crtc_power_domains(). Remove the incorrect get ref from the DSI
encoder hook.

Fixes: 2b68392e ("drm/i915/dsi: add support for DSC")
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201209153952.3397959-1-imre.deak@intel.com
(cherry picked from commit 3a9ec563)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>