p54: update MAINTAINERS

Michael has been out of the scene for a while now,
but despite Michael's absence, p54 is still maintained.

Cc: Michael Wu <aluminum.tape@gmail.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>