Fix the license header of hkdf
Change the license header of `hkdf.h` to a format the that script
`apache_to_gpl.pl` knows how to parse.
* specified by RFC 5869.
*/
/*
- * Copyright (C) 2016-2018, ARM Limited, All Rights Reserved
+ * Copyright (C) 2018-2019, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
