regulator: hi6421v530: Describe consumed platform device

The hi6421v530-regulator driver consumes a similarly named platform device.
Adding that to the module device table, allows modprobe to locate this
driver once the device is created.

Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>