xhci: only update dequeue ptr on completed transfers

The dequeue pointer should only be updated in case the transfer
is actually completed.  If we update it for inflight transfers
we will not pick them up again after migration, which easily
triggers with HID devices as they typically have a pending
transfer, waiting for user input to happen.

Fixes: 243afe85
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451631


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Message-id: 20170608074122.32099-1-kraxel@redhat.com