LSM: fix return value check in safesetid_init_securityfs()

In case of error, the function securityfs_create_dir() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check should
be replaced with IS_ERR().

Fixes: aeca4e2c ("LSM: add SafeSetID module that gates setid calls")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

security/safesetid/securityfs.c

@@ -167,7 +167,7 @@ static int __init safesetid_init_securityfs(void)
 		return 0;
 
 	safesetid_policy_dir = securityfs_create_dir("safesetid", NULL);
-	if (!safesetid_policy_dir) {
+	if (IS_ERR(safesetid_policy_dir)) {
 		ret = PTR_ERR(safesetid_policy_dir);
 		goto error;
 	}