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/audio_calibration.c b/dsp/audio_calibration.c
index 93bd352..a5167be 100644
--- a/dsp/audio_calibration.c
+++ b/dsp/audio_calibration.c
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2014, 2016-2017, The Linux Foundation. All rights reserved.
  */