staging: hikey9xx: hi6421v600-regulator: do some cleanups

Use C99 comments at the beginning of the file and remove
uneeded includes.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/cc0017d65b49ceb7df0357cec3a2dc1c4c2a118d.1611212783.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>