asoc: Update file header to GPL-2.0-only

Update file header to GPL-2.0-only.

Change-Id: If16bf92f951c6d7521f56a3e9b91da2ca2ccf6f8
Signed-off-by: Meng Wang <mengw@codeaurora.org>

asoc/kona.c

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2016-2019, The Linux Foundation. All rights reserved.
  */