Fix gvir_config_domain_sound_set_model
Fix gvir_config_domain_sound_set_model

It's creating an unwanted extra <sound> XML node:
<sound>
  <sound model="xxx">
</sound>
instead of the correct
<sound model="xxx">

JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,libvirt/libvirt-glib,JGulic/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib