mt76: Off by one in mt76_calc_rx_airtime()

The sband->bitrates[] array has "sband->n_bitrates" elements so this
check needs to be >= instead of > or we could read beyond the end of the
array.

These values come from when we call mt76_register_device():

	ret = mt76_register_device(&dev->mt76, true, mt7603_rates,
				   ARRAY_SIZE(mt7603_rates));

Here sband->bitrates[] is mt7603_rates[] and ->n_bitrates is the
ARRAY_SIZE()

Fixes: 5ce09c1 ("mt76: track rx airtime for airtime fairness and survey")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

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

@@ -242,7 +242,7 @@ u32 mt76_calc_rx_airtime(struct mt76_dev *dev, struct mt76_rx_status *status,
 			return 0;
 
 		sband = dev->hw->wiphy->bands[status->band];
-		if (!sband || status->rate_idx > sband->n_bitrates)
+		if (!sband || status->rate_idx >= sband->n_bitrates)
 			return 0;
 
 		rate = &sband->bitrates[status->rate_idx];