dm: sunxi: Linksprite_pcDuino3: Correct polarity of MMC card detect

This is shown as active high in the schematics[1], so fix it.

[1] https://patchwork.ozlabs.org/patch/777890/



Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>