vdpa_sim: reset must not run

vdpasim_do_reset sets running to true, which is wrong, as it allows
vdpasim_kick_vq to post work requests before the device has been
configured.  To fix, do not set running until VIRTIO_CONFIG_S_DRIVER_OK
is set.

Fixes: 0c89e2a3 ("vdpa_sim: Implement suspend vdpa op")
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <1707517807-137331-1-git-send-email-steven.sistare@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>