mmc: sunxi: Move the reset deassertion before enabling the clocks

As per Allwinner guidelines, the reset line should be deasserted before
turning the clocks on.

Implement it in our driver as well.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>