firmware: ti_sci: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in header file related to Firmware Drivers for Texas
Instruments SCI Protocol.
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 <[e-mail]>
Signed-off-by: Nishad Kamdar <[e-mail]>
Reviewed-by: Lokesh Vutla <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/firmware/ti_sci.h

···
-// SPDX-License-Identifier: BSD-3-Clause
+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
  * Texas Instruments System Control Interface (TISCI) Protocol
  *