asoc: Update file header to GPL-2.0-only

Update file header to GPL-2.0-only.

Change-Id: Ic1542a3209a5fe73c937a5b36491ede4a451936d
Signed-off-by: Meng Wang <mengw@codeaurora.org>
diff --git a/asoc/codecs/audio-ext-clk-up.c b/asoc/codecs/audio-ext-clk-up.c
index 74ab9e2..0d95ff1 100644
--- a/asoc/codecs/audio-ext-clk-up.c
+++ b/asoc/codecs/audio-ext-clk-up.c
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /* Copyright (c) 2015-2018, The Linux Foundation. All rights reserved.
  */