To get the number of address cells and size cells we have to use
the newly created partition node, not the parent device node. The
parent device node returns the address/size cells of the controller
node, not the partition node.

On an am335x machine this fixes the device tree passed to Linux.
The situation there is:
	...
	gpmc@50000000 {
		...
		#address-cells = <0x2>;
		#size-cells = <0x1>;
		ranges = <0x0 0x0 0x8000000 0x10000000>;
		...
		nand@0,0 {
			reg = <0x0 0x0 0x0>;
			#address-cells = <0x1>;
			#size-cells = <0x1>;
			...
			partition@7 {
				label = "system";
				reg = <0x220000 0x7de0000>;
			};
		};
	};

and without this patch barebox passes three bytes for
partition@7's reg property instead of only two which naturally
confuses Linux and yields to the system partition to start at 0
with a size of 0x220000.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>