drm/i915/dsb: Skip DSB command buffer setup if we have no LUTs

If we have no LUTs to load there is no point in setting up
the DSB command buffer.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230118163040.29808-9-ville.syrjala@linux.intel.com


Reviewed-by: Animesh Manna <animesh.manna@intel.com>