siox: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in
header file related to Eckelmann SIOX driver.
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/2019/2/7/46.

Suggested-by: Joe Perches <[email protected]>
Signed-off-by: Nishad Kamdar <[email protected]>
Acked-by: Uwe Kleine-König <[email protected]>
Acked-by: Thorsten Scherer <[email protected]>
Link: https://lore.kernel.org/r/20200101131418.GA3110@nishad
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: nishadkamdar

drivers/siox/siox.h

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <[email protected]>
  */