virtio_net: sparse annotation fix

offloads is a buffer in virtio format, should use
the __virtio64 tag.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -155,7 +155,7 @@ struct control_buf {
 	u8 promisc;
 	u8 allmulti;
 	__virtio16 vid;
-	u64 offloads;
+	__virtio64 offloads;
 };
 
 struct virtnet_info {