mt76: mt7615: Fix memory leak in mt7615_mcu_wtbl_sta_add()

In mt7615_mcu_wtbl_sta_add(), an skb sskb is allocated. If the
subsequent call to mt76_connac_mcu_alloc_wtbl_req() fails, the function
returns an error without freeing sskb, leading to a memory leak.

Fix this by calling dev_kfree_skb() on sskb in the error handling path
to ensure it is properly released.

Fixes: 99c457d ("mt76: mt7615: move mt7615_mcu_set_bmc to mt7615_mcu_ops")
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20251113062415.103611-1-zilin@seu.edu.cn
Signed-off-by: Felix Fietkau <nbd@nbd.name>

Author: GoodLuck612

drivers/net/wireless/mediatek/mt76/mt7615/mcu.c

@@ -874,8 +874,10 @@ mt7615_mcu_wtbl_sta_add(struct mt7615_phy *phy, struct ieee80211_vif *vif,
 	wtbl_hdr = mt76_connac_mcu_alloc_wtbl_req(&dev->mt76, &msta->wcid,
 						  WTBL_RESET_AND_SET, NULL,
 						  &wskb);
-	if (IS_ERR(wtbl_hdr))
+	if (IS_ERR(wtbl_hdr)) {
+		dev_kfree_skb(sskb);
 		return PTR_ERR(wtbl_hdr);
+	}
 
 	if (enable) {
 		mt76_connac_mcu_wtbl_generic_tlv(&dev->mt76, wskb, vif, sta,