ath5k: drop bogus warning on drv_set_key with unsupported cipher

Simply return -EOPNOTSUPP instead.

Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath5k/mac80211-ops.c

@@ -502,8 +502,7 @@ ath5k_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 			break;
 		return -EOPNOTSUPP;
 	default:
-		WARN_ON(1);
-		return -EINVAL;
+		return -EOPNOTSUPP;
 	}
 
 	mutex_lock(&ah->lock);