mmc: meson-gx: simplify usage of mmc_regulator_set_ocr

After 087592395a96 ("mmc: core: Allow invalid regulator in
mmc_regulator_set_ocr()") we can remove the checks here.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/858a592b-ebf4-99b4-74fc-21b4ad3382f8@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>