netlabel: Fix compiler warnings in netlabel_mgmt.c

Fix the compiler warnings below, thanks to Andrew Morton for finding them.

 net/netlabel/netlabel_mgmt.c: In function `netlbl_mgmt_listentry':
 net/netlabel/netlabel_mgmt.c:268: warning: 'ret_val' might be used
  uninitialized in this function
Signed-off-by: Paul Moore <paul.moore@hp.com>

net/netlabel/netlabel_mgmt.c

@@ -265,7 +265,7 @@ static int netlbl_mgmt_add_common(struct genl_info *info,
 static int netlbl_mgmt_listentry(struct sk_buff *skb,
 				 struct netlbl_dom_map *entry)
 {
-	int ret_val;
+	int ret_val = 0;
 	struct nlattr *nla_a;
 	struct nlattr *nla_b;
 	struct netlbl_af4list *iter4;