MAINTAINERS: Update bnx2x maintainer

Ariel Elior will take over the bnx2x maintenance.

It's been a pleasure!

Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Acked-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>