drm: edid revision 0 is valid

edid->revision == 0 should be valid (at least, so the error message
indicates. :) and wikipedia seems to indicate that EDID 1.0 existed.

We can dump the entire check, since edid->revision is a u8, so
it can't ever be less than 0.

Marko reports in RH bz#476735 that his monitor claims to be
EDID 1.0, and therefore hits the check and is stuck at 800x600 because
of it.

Reported-by: Marko Ristola <marko.ristola@kolumbus.fi>
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>