wifi: mt76: mt7921: fix NULL pointer access in mt7921_ipv6_addr_change

When disabling wifi mt7921_ipv6_addr_change() is called as a notifier.
At this point mvif->phy is already NULL so we cannot use it here.

Signed-off-by: Bert Karwatzki <spasswolf@web.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240812104542.80760-1-spasswolf@web.de

Author: spasswolf

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

@@ -1183,7 +1183,7 @@ static void mt7921_ipv6_addr_change(struct ieee80211_hw *hw,
 				    struct inet6_dev *idev)
 {
 	struct mt792x_vif *mvif = (struct mt792x_vif *)vif->drv_priv;
-	struct mt792x_dev *dev = mvif->phy->dev;
+	struct mt792x_dev *dev = mt792x_hw_dev(hw);
 	struct inet6_ifaddr *ifa;
 	struct in6_addr ns_addrs[IEEE80211_BSS_ARP_ADDR_LIST_LEN];
 	struct sk_buff *skb;