vhost-user-i2c: Back up vqs before cleaning up vhost_dev

vhost-user-i2c: Back up vqs before cleaning up vhost_dev

vhost_dev_cleanup() clears vhost_dev so back up its vqs member to free
the memory pointed by the member.

Fixes: 7221d3b634 ("hw/virtio: add boilerplate for vhost-user-i2c device")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20230130140435.78049-1-akihiko.odaki@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 0126793bee853e7c134627f51d2de5428a612e99)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>