odroid-go2: fix default FDT file path

The path in the Linux kernel dts directory is
rockchip/rk3326-odroid-go2.dtb.

That also seems to match the FDT path set on other boards (ie:
rock64-rk3328 for example).

Signed-off-by: Roger Pau Monne <royger@FreeBSD.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>