MAINTAINERS: add myself as Renesas R-Car SATA driver reviewer

Add myself as a reviewer for the Renesas R-Car SATA driver -- I don't have
the hardware anymore (Geert Uytterhoeven does have a lot of hardware!) but
I do have the manuals still! :-)

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>