staging: hikey9xx: hi6421v600-regulator: cleanup comments

Remove obvious comments and fix the comment for the
HI6421V600_LDO() macro.

While on it, use kernel-doc notation for HI6421V600_LDO(),
as kernel-doc can check if the arguments match its
description.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/d5e6dbdee5f7e143300249251ddbe09fdf64e669.1611212783.git.mchehab+huawei@kernel.org


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