vfio/ccw: Make vfio_ccw_register_irq_notifier() return a bool Since vfio_ccw_register_irq_notifier() takes an 'Error **' argument, best practices suggest to return a bool. See the qapi/error.h Rules section. Reviewed-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Farman <farman@linux.ibm.com> Signed-off-by: Cédric Le Goater <clg@redhat.com>