qdev: Fix device_add DRIVER,help to print to monitor

qdev: Fix device_add DRIVER,help to print to monitor

Help on device properties gets printed to stdout instead of the
monitor.  If you have the monitor anywhere else, no help for you.
Broken when commit e1043d674d "qdev: use object_property_help()"
accidentally switched from qemu_printf() to printf().  Switch right
back.

Fixes: e1043d674d792ff64aebae1a3eafc08b38a8a085
Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200714160202.3121879-2-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>