net: wwan: t7xx: Fix return type of t7xx_ccmni_start_xmit

net: wwan: t7xx: Fix return type of t7xx_ccmni_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 t7xx_ccmni_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>
Acked-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Link: https://lore.kernel.org/r/20220912214510.929070-1-nhuck@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>