Despite only mute being supported in this driver, set_stream_volumes()
is called whenever the volume info is changed to match the other drivers
and to allow a more complete volume implementation in the future.

The implementation will eventually move to the unixlib.
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Andrew Eikum <aeikum@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>