drm/i915: skip the i2c element in the generic VBT DSI driver

Don't choke on unknown elements when we do know how to skip them.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452518948-16469-1-git-send-email-jani.nikula@intel.com