Fixes gcc '-Wunused-but-set-variable' warning:
drivers/net/wireless/ath/carl9170/usb.c: In function carl9170_usb_disconnect:
drivers/net/wireless/ath/carl9170/usb.c:1110:21:
 warning: variable udev set but not used [-Wunused-but-set-variable]
It is not use since commit 
feb09b293327 ("carl9170:
fix misuse of device driver API")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
 static void carl9170_usb_disconnect(struct usb_interface *intf)
 {
        struct ar9170 *ar = usb_get_intfdata(intf);
-       struct usb_device *udev;
 
        if (WARN_ON(!ar))
                return;
 
-       udev = ar->udev;
        wait_for_completion(&ar->fw_load_wait);
 
        if (IS_INITIALIZED(ar)) {