mt76: fix possible NULL pointer dereference in mt76_tx

stable inclusion
from stable-5.10.50
commit 6987ee9bf0a2c06e0f19c0c2fdd340aec4260970
bugzilla: 174522 https://gitee.com/openeuler/kernel/issues/I4DNFY

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6987ee9bf0a2c06e0f19c0c2fdd340aec4260970

--------------------------------

[ Upstream commit d7400a2f ]

Even if this is not a real issue since mt76_tx is never run with wcid set
to NULL, fix a theoretical NULL pointer dereference in mt76_tx routine

Fixes: db9f11d3 ("mt76: store wcid tx rate info in one u32 reduce locking")
Signed-off-by: NLorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: NFelix Fietkau <nbd@nbd.name>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/net/wireless/mediatek/mt76/tx.c

@@ -278,7 +278,7 @@ mt76_tx(struct mt76_phy *phy, struct ieee80211_sta *sta,
 		skb_set_queue_mapping(skb, qid);
 	}
 
-	if (!(wcid->tx_info & MT_WCID_TX_INFO_SET))
+	if (wcid && !(wcid->tx_info & MT_WCID_TX_INFO_SET))
 		ieee80211_get_tx_rates(info->control.vif, sta, skb,
 				       info->control.rates, 1);