[U-Boot] rockchip: rk3288: fix EMMC_DIV_MASK definition in header

[Philipp Tomsich]

> It shoulb be '<<' instead of '<' for _MASK definition, fix it.
> 
> Signed-off-by: Ziyuan Xu <xzy.xu at rock-chips.com>
> Signed-off-by: Kever Yang <kever.yang at rock-chips.com>
> ---
> 
>  arch/arm/include/asm/arch-rockchip/cru_rk3288.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

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