regulator: Copy config passed during registration

Copy the 'regulator_config' structure passed to regulator_register()
function so the driver could safely modify it after parsing init data.

The driver may want to change the config as a result of specific init
data parsed by regulator core (e.g. when core handled parsing device
tree).

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>