vhost: remove unused paramete

"enabled" is defined in vhost_init_device_iotlb,
but it is never used. Let's remove it.

Signed-off-by: Liming Wu <liming.wu@jaguarmicro.com>
Message-Id: <20230110024445.303-1-liming.wu@jaguarmicro.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>