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>
diff --git a/dsp/q6adm.c b/dsp/q6adm.c
index 1851b98..688012f 100644
--- a/dsp/q6adm.c
+++ b/dsp/q6adm.c
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2012-2019, The Linux Foundation. All rights reserved.
  */