console: add & use qemu_console_lookup_by_device_name We have two places needing this, and a third one will come shortly. So factor things out into a helper function to reduce code duplication. Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com>