Pass oldDev to virDomainDefCompatibleDevice on device update
    
    When calling virDomainDefCompatibleDevice to check a new device during
    device update, we need to pass the original device which is going to be
    updated in addition to the new device. Otherwise, the function can
    report false conflicts.
    
    The new argument is currently ignored by virDomainDefCompatibleDevice,
    but this will change in the following patch.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1546971
    
    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>