vhost/vsock: handle vhost_vq_init_access() error

[ Upstream commit 0516ffd88fa0d006ee80389ce14a9ca5ae45e845 ]

Propagate the error when vhost_vq_init_access() fails and set
vq->private_data to NULL.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>