p54: fix p54_set_key's return code

p54 doesn't support AES-128-CMAC offload.

This patch will fix the noisy mac80211 warnings, when 802.11w is enabled:
mac80211-phy189: failed to set key (4, ff:ff:ff:ff:ff:ff) to hardware (-22)
mac80211-phy189: failed to set key (5, ff:ff:ff:ff:ff:ff) to hardware (-22)
Signed-off-by: NChristian Lamparter <chunkeey@web.de>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/p54common.c

@@ -2077,7 +2077,7 @@ static int p54_set_key(struct ieee80211_hw *dev, enum set_key_cmd cmd,
 			algo = P54_CRYPTO_AESCCMP;
 			break;
 		default:
-			return -EINVAL;
+			return -EOPNOTSUPP;
 		}
 	}