ravb: Fix use-after-free issue in ravb_tx_timeout_work()

The ravb_stop() should call cancel_work_sync(). Otherwise,
ravb_tx_timeout_work() is possible to use the freed priv after
ravb_remove() was called like below:

CPU0			CPU1
			ravb_tx_timeout()
ravb_remove()
unregister_netdev()
free_netdev(ndev)
// free priv
			ravb_tx_timeout_work()
			// use priv

unregister_netdev() will call .ndo_stop() so that ravb_stop() is
called. And, after phy_stop() is called, netif_carrier_off()
is also called. So that .ndo_tx_timeout() will not be called
after phy_stop().

Fixes: c156633f ("Renesas Ethernet AVB driver proper")
Reported-by: Zheng Wang <zyytlz.wz@163.com>
Closes: https://lore.kernel.org/netdev/20230725030026.1664873-1-zyytlz.wz@163.com/Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/20231005011201.14368-3-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/renesas/ravb_main.c

@@ -2167,6 +2167,8 @@ static int ravb_close(struct net_device *ndev)
 			of_phy_deregister_fixed_link(np);
 	}
 
+	cancel_work_sync(&priv->work);
+
 	if (info->multi_irqs) {
 		free_irq(priv->tx_irqs[RAVB_NC], ndev);
 		free_irq(priv->rx_irqs[RAVB_NC], ndev);