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/soc/regmap-swr.c b/soc/regmap-swr.c
index 7f00aab..4d8fbb8 100644
--- a/soc/regmap-swr.c
+++ b/soc/regmap-swr.c
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2015-2017, The Linux Foundation. All rights reserved.
  */