- clarify license version (it should be GPL 2.0)
- use SPDX header

Cc: Michael Schmitz <schmitzmic@gmail.com>
Acked-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NBartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: NTejun Heo <tj@kernel.org>