drm: fix EDID backward compat check

EDIDs should be backward compatible, so don't bail if we see a version
of 3 (which is out there now) and print a message if we see something
newer, but allow it to be parsed.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>