staging: regulator: hi6421v600-regulator: coding style fixups

There are several issues on those drivers related to their
coding style. Solve most of them.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9ea7fdc004c7c44ae513b6c8f6c4a4493dd1ac61.1597647359.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>