[U-Boot] rockchip: dts: firefly using ddr3 1600

[Philipp Tomsich]

> According to my test, some of firefly-rk3399 hang after dram init
> when using ddr3-1333 config, while using ddr3-1600 config works
> for all the board I have test.
> 
> Signed-off-by: Kever Yang <kever.yang at rock-chips.com>
> Acked-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  arch/arm/dts/rk3399-firefly.dts | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Applied to u-boot-rockchip, thanks!