Use correct default audio output and input devices on Windows.

It was returning the first available device as the default, which might
not be the actual default device. Use the WAVE_MAPPER device ID instead
that tells Windows to use the most appropriate device.

Change-Id: Id1e9324e889bbaaab54bc0e0da810a7ce5fcb592
Reviewed-by: Andy Nichols <andy.nichols@digia.com>