mt76: mt7615: remove unused variable in mt7615_mcu_set_bcn

Remove tim_len in mt7615_mcu_set_bcn since it is not actually used
and ieee80211_beacon_get_tim checks if tim_length is NULL
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -1129,10 +1129,10 @@ int mt7615_mcu_set_bcn(struct mt7615_dev *dev, struct ieee80211_vif *vif,
 		/* pky_type: 0 for bcn, 1 for tim */
 		.pkt_type = 0,
 	};
-	u16 tim_off, tim_len;
 	struct sk_buff *skb;
+	u16 tim_off;
 
-	skb = ieee80211_beacon_get_tim(mt76_hw(dev), vif, &tim_off, &tim_len);
+	skb = ieee80211_beacon_get_tim(mt76_hw(dev), vif, &tim_off, NULL);
 	if (!skb)
 		return -EINVAL;