[U-Boot] rockchip: rk3288: update the mmc number for fastboot

[Philipp Tomsich]

> The emmc number is 0, correct it for fastboot parameter.
> 
> Signed-off-by: Kever Yang <kever.yang at rock-chips.com>
> ---
> 
>  include/configs/rk3288_common.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

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