mt76: mt7915: fix memory leak in mt7915_mcu_get_rx_rate()

Free the skb to prevent memory leak.
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -3541,5 +3541,7 @@ int mt7915_mcu_get_rx_rate(struct mt7915_phy *phy, struct ieee80211_vif *vif,
 		break;
 	}
 
+	dev_kfree_skb(skb);
+
 	return 0;
 }