drm/xe: remove MISSING_CASE() from compat i915_utils.h
There are no longer users for MISSING_CASE() in the compat
i915_utils.h. Remove it to prevent new users from showing up.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/b967e605ff9d9ad459f3d12a9dfc9244458d83a1.1763578288.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>