doc: renesas: Update code owner for Renesas platforms

Add Marek Vasut as the code owner for the common code shared by
both Renesas R-Car and RZ/G2 platforms.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Change-Id: I3c0a402f4663ffcf4d2df408a3ccd4d1a8629b3a
1 file changed