ARM: dts: at91: nattis: make the SD-card slot work

The cd-gpios signal is assumed active-low by the driver, and the
cd-inverted property is needed if it is, in fact, active-high. Fix
this oversight.

Fixes: 0e432389 ("ARM: dts: at91: add devicetree for the Axentia Nattis with Natte power")
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>