If the queue PFN is set to zero on a virtio-mmio device, the device is reset.
In that case however the virtio_bus_stop_ioeventfd function was not
called; add it so that the behavior is similar to when status is set to 0.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>