regulator: hi6421v600: use lowercase for ldo

As lowercase is generally preferred for node names, while it is
not too late, change the LDO DT properties to lower case.

Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/395510cffeb39aebd1763cc5de1cb00a2c40e461.1627121912.git.mchehab+huawei@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>