drm/i915/display: Fix the dsc check while selecting min_cdclk

The right parameter that selects second dsc engine is dsc_split.
Hence use dsc_split instead of slice_count while selecting the
cdclk in order to accommodate 1ppc limitaion of vdsc.

Fixes: fe01883f

 ("drm/i915: Get proper min cdclk if vDSC enabled")
Suggested-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210915054338.29869-1-vandita.kulkarni@intel.com