vhost: use unsigned int for nvqs

Switch to use unsigned int for nvqs since it's not expected to be
negative.

Reviewed-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20210903091031.47303-5-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/hw/virtio/vhost.h

@@ -71,7 +71,7 @@ struct vhost_dev {
     int n_tmp_sections;
     MemoryRegionSection *tmp_sections;
     struct vhost_virtqueue *vqs;
-    int nvqs;
+    unsigned int nvqs;
     /* the first virtqueue which would be used by this vhost dev */
     int vq_index;
     /* if non-zero, minimum required value for max_queues */