regulator: stw481x-vmmc: use devm_regulator_register()

Use devm_regulator_register() to make cleanup paths simpler,
and remove unnecessary remove().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>