mmc: sunxi: Return error on mmc_regulator_set_ocr() fail in .set_ios op

Let .set_ios() fail if mmc_regulator_set_ocr() fails to enable and set a
proper voltage for vmmc.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>