intel_th: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in header files related to Drivers for Intel(R) Trace Hub
controller.
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/intel_th/msu.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Intel(R) Trace Hub Memory Storage Unit (MSU) data structures
  *

drivers/hwtracing/intel_th/pti.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Intel(R) Trace Hub PTI output data structures
  *