MAINTAINERS: drop Michael from bfin_mac driver

We want people to just use the list now rather than hitting up people
who are no longer responsible for it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>