rockchip: evb-rk3399: correct README for board bring up

%s/rkflashtool/rkdeveloptool/

We are using rkdeveloptool not rkflashtool.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed