ath5k: drop bogus warning on drv_set_key with unsupported cipher

BugLink: http://bugs.launchpad.net/bugs/1673538

commit a70e1d6f upstream.

Simply return -EOPNOTSUPP instead.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.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);