dt-bindings: arm: rockchip: Correct vendor for Orange Pi RK3399 board

The vendor for this board was incorrectly listed as Rockchip. Fix this
now while they are not used anywhere, in the future they may be used by
bootloader to select dts.

Update the vendor to Xunlong.

Signed-off-by: Tim Lunn <tim@feathertop.org>
Fixes: 08b64bd2 ("arm64: dts: rockchip: Add support for the Orange  Pi RK3399 board")
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240214040731.3069111-2-tim@feathertop.org


Signed-off-by: Heiko Stuebner <heiko@sntech.de>