ohci: relax link check

The strict td link limit added by commit "95ed569 usb: ohci: limit the
number of link eds" causes problems with macos guests.  Lets raise the
limit.

Reported-by: Programmingkid <programmingkidx@gmail.com>
Reported-by: Howard Spoelstra <hsp.cat7@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: John Arbuckle <programmingkidx@gmail.com>
Message-id: 1488876018-31576-1-git-send-email-kraxel@redhat.com
