[U-Boot] rockchip: configs: fix typo in BOOT_TARGET_DEVICES

[Philipp Tomsich]

> dchp should be dhcp. fixed copy-paste versions too.
> 
> Signed-off-by: Klaus Goger <klaus.goger at theobroma-systems.com>
> ---
> 
>  include/configs/rockchip-common.h | 4 ++--
>  include/configs/tinker_rk3288.h   | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>