core: fix sound device check when adding devices from ovf (#1004066)

When creating vm from ovf, there is a check to add sound device to the
vm if it doesn't exist and needed.
the existence check was wrong as it used 'device' compared with 'type'.

this patch fix the check to use the correct fields (type).

Change-Id: I117c18f95db1ed672f6d0a8c4ff5c003d3fb6d4a
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1004066