ARM: dts: kirkwood: fix pin names for UART/SD selection for OpenRD

The UART/SD pin names are swapped, fix that.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>