regulator: core: Fix voltage change propagations to supply regulators

Some regulators support get_voltage() and some support get_voltage_sel()
operations but currently we only propagate changes if the regulator has
a get_voltage() operation.  Also do this if we've got get_voltage_sel()

[Rewite commit message for clarity -- broonie]

Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>