apparmor: Fix memory leak of rule on error exit path

Currently on the error exit path the allocated rule is not free'd
causing a memory leak. Fix this by calling aa_audit_rule_free().

Detected by CoverityScan, CID#1468966 ("Resource leaks")

Fixes: cb740f574c7b ("apparmor: modify audit rule support to support profile stacks")
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/audit.c

@@ -200,10 +200,12 @@ int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
 	/* Currently rules are treated as coming from the root ns */
 	rule->label = aa_label_parse(&root_ns->unconfined->label, rulestr,
 				     GFP_KERNEL, true, false);
-	if (IS_ERR(rule->label))
+	if (IS_ERR(rule->label)) {
+		aa_audit_rule_free(rule);
 		return PTR_ERR(rule->label);
-	*vrule = rule;
+	}
 
+	*vrule = rule;
 	return 0;
 }