udldrmfb: udl_get_edid: drop unneeded i--

This is a left-over from when udl_get_edid returned the amount of bytes
successfully read, which it no longer does.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>