ep93xx_eth: Update MAINTAINERS

Lennert stated that he has been short on time lately. Since I'm maintaining
the ep93xx core stuff, I'm willing to also take over maintaining the Ethernet
driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Mika Westerberg <mika.westerberg@iki.fi>
Acked-by: Lennert Buytenhek <kernel@wantstofly.org>
Signed-off-by: David S. Miller <davem@davemloft.net>