MAINTAINERS: review Renesas DT bindings as well

When adding myself  as a reviewer for  the Renesas  Ethernet drivers
I somehow forgot about the bindings -- I want to review them as well.

Fixes: 8e6569af ("MAINTAINERS: add myself as Renesas Ethernet drivers reviewer")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>