[U-Boot] [U-Boot, 1/1] rockchip: evb-rk3399: correct README for board bring up

[Philipp Tomsich]

> %s/rkflashtool/rkdeveloptool/
> 
> We are using rkdeveloptool not rkflashtool.
> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> Acked-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> Reviewed-by: Kever Yang <kever.yang at rock-chips.com>
> ---
>  board/rockchip/evb_rk3399/README | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Applied to u-boot-rockchip, thanks!