MAINTAINERS: ASP 2.0 Ethernet driver maintainers

Add maintainers entry for ASP 2.0 Ethernet driver.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>