drm/edid: constify edid quirk list

No reason not to be const.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1482923186-22430-1-git-send-email-jani.nikula@intel.com