staging: brcm80211: updated MAINTAINERS, README and TODO files

README now only contains a link to the brcm80211 driver page. Two maintainers
have been added, one deleted. TODO file has also been updated.

Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>