wifi: rtw89: fix leak in rtw89_core_send_nullfunc()

If there is no rtwsta_link found in rtw89_core_send_nullfunc(), allocated
skb is leaked.  Free it on the error handling path.

Found by Linux Verification Center (linuxtesting.org).

Fixes: a8ba4ac ("wifi: rtw89: send nullfunc based on the given link")
Signed-off-by: Fedor Pchelkin <[email protected]>
Acked-by: Ping-Ke Shih <[email protected]>
Signed-off-by: Ping-Ke Shih <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: pchelkin91

drivers/net/wireless/realtek/rtw89/core.c

@@ -3961,6 +3961,7 @@ int rtw89_core_send_nullfunc(struct rtw89_dev *rtwdev, struct rtw89_vif_link *rt
 	rtwsta_link = rtwsta->links[rtwvif_link->link_id];
 	if (unlikely(!rtwsta_link)) {
 		ret = -ENOLINK;
+		dev_kfree_skb_any(skb);
 		goto out;
 	}