vdpa: Replace qemu_open_old by qemu_open at

vdpa: Replace qemu_open_old by qemu_open at

There is no reason to keep using the old one, since we neither use the
variadics arguments nor open it with O_DIRECT.

Also, net_client_init1, the caller of net_init_vhost_vdpa, wants all
net_client_init_fun to use Error API, so it's a good step in that
direction.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20211112193431.2379298-2-eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>