wifi: rtw88: usb: send Zero length packets if necessary

Zero length packets are necessary when sending URBs with size
multiple of bulkout_size, otherwise the hardware just stalls.

Fixes: a82dfd33 ("wifi: rtw88: Add common USB chip support")
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: NPing-Ke Shih <pkshih@realtek.com>
Signed-off-by: NKalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230210111632.1985205-3-s.hauer@pengutronix.de

drivers/net/wireless/realtek/rtw88/usb.c

@@ -271,6 +271,7 @@ static int rtw_usb_write_port(struct rtw_dev *rtwdev, u8 qsel, struct sk_buff *s
 		return -ENOMEM;
 
 	usb_fill_bulk_urb(urb, usbd, pipe, skb->data, skb->len, cb, context);
+	urb->transfer_flags |= URB_ZERO_PACKET;
 	ret = usb_submit_urb(urb, GFP_ATOMIC);
 
 	usb_free_urb(urb);