regulator: mc13xxx: Remove get_voltage implementation for single voltage regulators

This is not required after commit f7df20ec
"regulator: core: Use list_voltage() to read single voltage regulators"

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
4 files changed