apparmor: Use IS_ERR_OR_NULL() helper function

Use the IS_ERR_OR_NULL() helper instead of open-coding a
NULL and an error pointer checks to simplify the code and
improve readability.

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

Author: Hongbo Li

security/apparmor/path.c

@@ -130,7 +130,7 @@ static int d_namespace_path(const struct path *path, char *buf, char **name,
 	/* handle error conditions - and still allow a partial path to
 	 * be returned.
 	 */
-	if (!res || IS_ERR(res)) {
+	if (IS_ERR_OR_NULL(res)) {
 		if (PTR_ERR(res) == -ENAMETOOLONG) {
 			error = -ENAMETOOLONG;
 			*name = buf;