drm/i915/bios: cleanup comments and useless return

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4a95fb9d23d980830e3158d3c57258e6539965ce.1506586821.git.jani.nikula@intel.com