vdpasim: Return status in vdpasim_get_status

vdpasim->status should acquired under spin lock.

Fixes: 870448c31775 ("vdpasim: vDPA device simulator")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200402024916.35192-1-yuehaibing@huawei.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>