MAINTAINERS: raise status of 9p to 'Maintained'

MAINTAINERS: raise status of 9p to 'Maintained'

Change status of 9p from 'Odd Fixes' to 'Maintained', as this better
reflects current situation. I already take care of 9p patches for a
while, which included new features as well.

Based-on: <E1qDkmw-0007M1-8f@lizzy.crudebyte.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <E1qGKgV-0003Hj-01@lizzy.crudebyte.com>