net: davicom: Fix return type of dm9000_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 dm9000_start_xmit should be changed from int to
netdev_tx_t.

Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1703
Cc: llvm@lists.linux.dev
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20220912194722.809525-1-nhuck@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/davicom/dm9000.c

@@ -1011,7 +1011,7 @@ static void dm9000_send_packet(struct net_device *dev,
  *  Hardware start transmission.
  *  Send a packet to media from the upper layer.
  */
-static int
+static netdev_tx_t
 dm9000_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	unsigned long flags;