drm/i915/gmbus: whitespace cleanup in reg definitions

Simple whitespace cleanup and comment movement.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/50df38c9f3e53dba64429b7eaa6c0d7bfaf74078.1661855191.git.jani.nikula@intel.com