netfilter: x_tables: unlock on error in xt_find_table_lock()

According to my static checker we should unlock here before the return.
That seems reasonable to me as well.

Fixes" b9e69e12 ("netfilter: xtables: don't hook tables by default")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/x_tables.c

@@ -1051,8 +1051,10 @@ struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
 	list_for_each_entry(t, &init_net.xt.tables[af], list) {
 		if (strcmp(t->name, name))
 			continue;
-		if (!try_module_get(t->me))
+		if (!try_module_get(t->me)) {
+			mutex_unlock(&xt[af].mutex);
 			return NULL;
+		}
 
 		mutex_unlock(&xt[af].mutex);
 		if (t->table_init(net) != 0) {