mt76: mt76x02: fix coverage_class type

Fix coverage_class type in mt76x02_dev data structure since
coverage_class can be negative to enable dynack (just supported by
ath9k). Set 0 as minimum value for coverage_class

Fixes: 7bc04215 ("mt76: add driver code for MT76x2e")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76x02.h

@@ -116,7 +116,7 @@ struct mt76x02_dev {
 
 	bool no_2ghz;
 
-	u8 coverage_class;
+	s16 coverage_class;
 	u8 slottime;
 
 	struct mt76x02_dfs_pattern_detector dfs_pd;

drivers/net/wireless/mediatek/mt76/mt76x02_util.c

@@ -545,7 +545,7 @@ void mt76x02_set_coverage_class(struct ieee80211_hw *hw,
 	struct mt76x02_dev *dev = hw->priv;
 
 	mutex_lock(&dev->mt76.mutex);
-	dev->coverage_class = coverage_class;
+	dev->coverage_class = max_t(s16, coverage_class, 0);
 	mt76x02_set_tx_ackto(dev);
 	mutex_unlock(&dev->mt76.mutex);
 }