staging: regulator: hi6421v600-regulator: code cleanup

Do some code cleanup in order to make it cleaner for moving
it out of staging in the future.

Suggested-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/32fadb359c1817992af78052e2d9448b8c5fc61f.1597647359.git.mchehab+huawei@kernel.org


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