net: ethernet: litex: Fix return type of liteeth_start_xmit

The ndo_start_xmit field in net_device_ops is expected to be of type
netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb, struct net_device *dev).

The mismatched return type breaks forward edge kCFI since the underlying
function definition does not match the function hook definition.

The return type of liteeth_start_xmit should be changed from int to
netdev_tx_t.

Reported-by: Dan Carpenter <[e-mail]>
Link: https://github.com/ClangBuiltLinux/linux/issues/1703
Cc: [e-mail]
Signed-off-by: Nathan Huckleberry <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Acked-by: Gabriel Somlo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/litex/litex_liteeth.c

···
 	return 0;
 }
 
-static int liteeth_start_xmit(struct sk_buff *skb, struct net_device *netdev)
+static netdev_tx_t liteeth_start_xmit(struct sk_buff *skb,
+				      struct net_device *netdev)
 {
 	struct liteeth *priv = netdev_priv(netdev);
 	void __iomem *txbuffer;