staging: r8188eu: Fix return type of rtw_xmit_entry

staging: r8188eu: Fix return type of rtw_xmit_entry

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 rtw_xmit_entry should be changed from int to
netdev_tx_t.

Link: https://github.com/ClangBuiltLinux/linux/issues/1703
Cc: llvm@lists.linux.dev
Reported-by: Dan Carpenter <error27@gmail.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Link: https://lore.kernel.org/r/20220914211606.423959-1-nhuck@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>