net/virtio: fix incorrect cast of void *

net/virtio: fix incorrect cast of void *

The rx_queues and tx_queues fields of the data structure points to a struct
virtnet_rx or virtnet_tx. Casting it to a virtqueue is an error.

It does not trigger any bug because pointer is not dereferenced inside the
function, but it can become a bug if this code is copy/pasted and vq is
dereferenced.

Fixes: 01ad44fd374f ("net/virtio: split Rx/Tx queue")
Cc: stable@dpdk.org
Signed-off-by: Didier Pallard <didier.pallard@6wind.com>
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>