drm/i915: Remove pointless dpll_funcs checks

All platforms have dpll_funcs. Remove the pointless NULL checks.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220325123205.22140-4-ville.syrjala@linux.intel.com


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