drm/i915/icl: Fix initing the DSI DSC power refcount during HW readout

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.

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