Load switches are modeled as regulators but they just provide
the voltage of their parent input supply. So, the drivers for
these switches usually neither provide a .list_voltage handler
not set a .n_voltages count. But there is code in the kernel
that assumes that all regulators should be able to provide this
information (e.g: cpufreq and mmc subsystems).

If the voltage count and list are not available for a regulator
and it has a parent input supply, then use the parent values.
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@linaro.org>