wifi: mt76: mt7921: fix reporting of TX AGGR histogram

Similar to mt7915, fix stats clash between bins [4-7] in 802.11 tx
aggregation histogram.

Fixes: 163f4d22 ("mt76: mt7921: add MAC support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/mac.c

@@ -984,7 +984,7 @@ void mt7921_mac_update_mib_stats(struct mt7921_phy *phy)
 		mib->tx_amsdu_cnt += val;
 	}
 
-	for (i = 0, aggr1 = aggr0 + 4; i < 4; i++) {
+	for (i = 0, aggr1 = aggr0 + 8; i < 4; i++) {
 		u32 val2;
 
 		val = mt76_rr(dev, MT_TX_AGG_CNT(0, i));