clk: renesas: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in header files related to Clock Drivers for Renesas Socs.
For C header files Documentation/process/license-rules.rst
mandates C-like comments (opposed to C source files where
C++ style should be used)

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/renesas/rcar-gen2-cpg.h

-/* SPDX-License-Identifier: GPL-2.0
- *
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
  * R-Car Gen2 Clock Pulse Generator
  *
  * Copyright (C) 2016 Cogent Embedded Inc.

drivers/clk/renesas/rcar-gen3-cpg.h

-/* SPDX-License-Identifier: GPL-2.0
- *
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
  * R-Car Gen3 Clock Pulse Generator
  *
  * Copyright (C) 2015-2018 Glider bvba

drivers/clk/renesas/renesas-cpg-mssr.h

-/* SPDX-License-Identifier: GPL-2.0
- *
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
  * Renesas Clock Pulse Generator / Module Standby and Software Reset
  *
  * Copyright (C) 2015 Glider bvba