mt76: mt7921: do not use 0 as NULL pointer

Fix the following sparse warning:
drivers/net/wireless/mediatek/mt76/mt7921/mac.c:1425:70:
  warning: Using plain integer as NULL pointer
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -1424,7 +1424,7 @@ void mt7921_mac_reset_work(struct work_struct *work)
 	ieee80211_wake_queues(hw);
 	ieee80211_iterate_active_interfaces(hw,
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
-					    mt7921_vif_connect_iter, 0);
+					    mt7921_vif_connect_iter, NULL);
 }
 
 void mt7921_reset(struct mt76_dev *mdev)