wifi: mt76: mt7996: fix insecure data handling of mt7996_mcu_rx_radar_detected()

Coverity message:
using tainted "r->band_idx" variable as an index into an array "(*dev).mt76.phys".
Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527812 ("Insecure data handling")
Fixes: 98686cd2 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi 7 (802.11be) devices")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7996/mcu.c

@@ -335,6 +335,9 @@ mt7996_mcu_rx_radar_detected(struct mt7996_dev *dev, struct sk_buff *skb)
 
 	r = (struct mt7996_mcu_rdd_report *)skb->data;
 
+	if (r->band_idx >= ARRAY_SIZE(dev->mt76.phys))
+		return;
+
 	mphy = dev->mt76.phys[r->band_idx];
 	if (!mphy)
 		return;