ui: Update MAINTAINERS entry.

With Amazon eating Anthonys time status "Maintained" certainly isn't
true any more.  Update entry accordingly.

Also add myself, so scripts/get_maintainer.pl will Cc: me, to reduce
the chance ui patches fall through the cracks on our pretty loaded
qemu-devel mailing list.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
