staging: regulator: hi6421v600-regulator: use shorter names for OF properties

Simplify the names of the OF properties, in order to make
them similar to other drivers and to make easier to understand
what each property means.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/98f66100263940901ba59ec187919e9cf5e64f31.1597647359.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>