ARM: dts: imx6ull: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in imx6ull-pinfunc-snvs.h.

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46
and making some manual changes.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6ull-pinfunc-snvs.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2016 Freescale Semiconductor, Inc.
  * Copyright (C) 2017 NXP