staging: most: dim2: reg.h: Correct SPDX-License-Identifier

Correct SPDX-License-Identifier comment characters to silence
checkpatch.pl warning:
WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
Signed-off-by: Wentao Cai <etsai042@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/dim2/reg.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * reg.h - Definitions for registers of DIM2
  * (MediaLB, Device Interface Macro IP, OS62420)