vdpa: fix gcc cvq_isolated uninitialized variable warning

vdpa: fix gcc cvq_isolated uninitialized variable warning

gcc 13.2.1 emits the following warning:

  net/vhost-vdpa.c: In function ‘net_vhost_vdpa_init.constprop’:
  net/vhost-vdpa.c:1394:25: error: ‘cvq_isolated’ may be used uninitialized [-Werror=maybe-uninitialized]
   1394 |         s->cvq_isolated = cvq_isolated;
        |         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
  net/vhost-vdpa.c:1355:9: note: ‘cvq_isolated’ was declared here
   1355 |     int cvq_isolated;
        |         ^~~~~~~~~~~~
  cc1: all warnings being treated as errors

Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230911215435.4156314-1-stefanha@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>