rtlwifi: Fix a double free in _rtl_usb_tx_urb_setup()

Seven years ago we tried to fix a leak but actually introduced a double
free instead. It was an understandable mistake because the code was a
bit confusing and the free was done in the wrong place. The "skb"
pointer is freed in both _rtl_usb_tx_urb_setup() and _rtl_usb_transmit().
The free belongs _rtl_usb_transmit() instead of _rtl_usb_tx_urb_setup()
and I've cleaned the code up a bit to hopefully make it more clear.

Fixes: 36ef0b473fbf ("rtlwifi: usb: add missing freeing of skbuff")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/20200513093951.GD347693@mwanda

drivers/net/wireless/realtek/rtlwifi/usb.c

···
 
 	WARN_ON(NULL == skb);
 	_urb = usb_alloc_urb(0, GFP_ATOMIC);
-	if (!_urb) {
-		kfree_skb(skb);
+	if (!_urb)
 		return NULL;
-	}
 	_rtl_install_trx_info(rtlusb, skb, ep_num);
 	usb_fill_bulk_urb(_urb, rtlusb->udev, usb_sndbulkpipe(rtlusb->udev,
 			  ep_num), skb->data, skb->len, _rtl_tx_complete, skb);
···
 	struct rtl_usb *rtlusb = rtl_usbdev(rtl_usbpriv(hw));
 	u32 ep_num;
 	struct urb *_urb = NULL;
-	struct sk_buff *_skb = NULL;
 
 	WARN_ON(NULL == rtlusb->usb_tx_aggregate_hdl);
 	if (unlikely(IS_USB_STOP(rtlusb))) {
···
 		return;
 	}
 	ep_num = rtlusb->ep_map.ep_mapping[qnum];
-	_skb = skb;
-	_urb = _rtl_usb_tx_urb_setup(hw, _skb, ep_num);
+	_urb = _rtl_usb_tx_urb_setup(hw, skb, ep_num);
 	if (unlikely(!_urb)) {
 		pr_err("Can't allocate urb. Drop skb!\n");
 		kfree_skb(skb);