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 e1043d67 "qdev: use object_property_help()"
accidentally switched from qemu_printf() to printf().  Switch right
back.

Fixes: e1043d67
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>