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.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>