[U-Boot] [U-Boot,2/3] rockchip: mmc: update MAINTAINERS

[Philipp Tomsich]

> The Rockchip-specific wrappers to the DW-MMC and the SDHCI driver
> were not covered as part of what's maintained by the architecture
> maintainers.  Add them here.
> 
> Signed-off-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  MAINTAINERS | 2 ++
>  1 file changed, 2 insertions(+)
> 

Applied to u-boot-rockchip, thanks!