wifi: mt76: mt7915: workaround too long expansion sparse warnings

Fix the following sparse warnings:

drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c:1133:29: error: too long token expansion
drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c:1133:29: error: too long token expansion
drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c:1133:29: error: too long token expansion
drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c:1133:29: error: too long token expansion

No functional changes, compile tested only.

Fixes: e329675 ("wifi: mt76: mt7915: enable per bandwidth power limit support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/5457b92e41909dd75ab3db7a0e9ec372b917a386.1710858172.git.lorenzo@kernel.org

drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c

@@ -1049,6 +1049,7 @@ static ssize_t
 mt7915_rate_txpower_set(struct file *file, const char __user *user_buf,
 			size_t count, loff_t *ppos)
 {
+	int i, ret, pwr, pwr160 = 0, pwr80 = 0, pwr40 = 0, pwr20 = 0;
 	struct mt7915_phy *phy = file->private_data;
 	struct mt7915_dev *dev = phy->dev;
 	struct mt76_phy *mphy = phy->mt76;
@@ -1057,7 +1058,6 @@ mt7915_rate_txpower_set(struct file *file, const char __user *user_buf,
 		.band_idx = phy->mt76->band_idx,
 	};
 	char buf[100];
-	int i, ret, pwr160 = 0, pwr80 = 0, pwr40 = 0, pwr20 = 0;
 	enum mac80211_rx_encoding mode;
 	u32 offs = 0, len = 0;
 
@@ -1130,8 +1130,8 @@ mt7915_rate_txpower_set(struct file *file, const char __user *user_buf,
 	if (ret)
 		goto out;
 
-	mphy->txpower_cur = max(mphy->txpower_cur,
-				max(pwr160, max(pwr80, max(pwr40, pwr20))));
+	pwr = max3(pwr80, pwr40, pwr20);
+	mphy->txpower_cur = max3(mphy->txpower_cur, pwr160, pwr);
 out:
 	mutex_unlock(&dev->mt76.mutex);