regulator: max1586: Remove regulator_dev pointer from state container

Don't store pointer to regulator_dev returned by
devm_regulator_register() in state container. It isn't used anywhere
outside of max1586_pmic_probe() function.

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