libertas: fix signedness bug in lbs_auth_to_authtype()

Return type for lbs_auth_to_authtype() is changed from "u8" to
"int" to return negative error code correctly.
Also an error check is added in connect handler for invalid auth
type.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/cfg.c

@@ -103,7 +103,7 @@ static const u32 cipher_suites[] = {
  * Convert NL80211's auth_type to the one from Libertas, see chapter 5.9.1
  * in the firmware spec
  */
-static u8 lbs_auth_to_authtype(enum nl80211_auth_type auth_type)
+static int lbs_auth_to_authtype(enum nl80211_auth_type auth_type)
 {
 	int ret = -ENOTSUPP;
 
@@ -1411,7 +1411,12 @@ static int lbs_cfg_connect(struct wiphy *wiphy, struct net_device *dev,
 		goto done;
 	}
 
-	lbs_set_authtype(priv, sme);
+	ret = lbs_set_authtype(priv, sme);
+	if (ret == -ENOTSUPP) {
+		wiphy_err(wiphy, "unsupported authtype 0x%x\n", sme->auth_type);
+		goto done;
+	}
+
 	lbs_set_radio(priv, preamble, 1);
 
 	/* Do the actual association */