wifi: mt76: mt7603: fix beacon interval after disabling a single vif

When disabling beacons on a vif, intval is 0. Ensure that dev->mt76.beacon_int
is not overwritten in this case, so that beacons continue to work for other
interfaces.
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7603/beacon.c

@@ -161,6 +161,7 @@ void mt7603_beacon_set_timer(struct mt7603_dev *dev, int idx, int intval)
 		return;
 	}
 
+	if (intval)
 		dev->mt76.beacon_int = intval;
 	mt76_wr(dev, MT_TBTT,
 		FIELD_PREP(MT_TBTT_PERIOD, intval) | MT_TBTT_CAL_ENABLE);