mt76: mt7615: Remove set but unused variable 'index'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/wireless/mediatek/mt76/mt7615/testmode.c: In function mt7615_tm_set_tx_power
drivers/net/wireless/mediatek/mt76/mt7615/testmode.c:83:7: warning: variable ‘index’ set but not used [-Wunused-but-set-variable]=

commit 4f0bce1c ("mt76: mt7615: implement testmode support")
involved this unused variable, remove it.
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7615/testmode.c

@@ -80,15 +80,12 @@ mt7615_tm_set_tx_power(struct mt7615_phy *phy)
 
 	target_chains = mt7615_ext_pa_enabled(dev, band) ? 1 : n_chains;
 	for (i = 0; i < target_chains; i++) {
-		int index;
-
 		ret = mt7615_eeprom_get_target_power_index(dev, chandef->chan, i);
 		if (ret < 0) {
 			dev_kfree_skb(skb);
 			return -EINVAL;
 		}
 
-		index = ret - MT_EE_NIC_CONF_0;
 		if (tx_power && tx_power[i])
 			data[ret - MT_EE_NIC_CONF_0] = tx_power[i];
 	}