mixer: only list playbackdevices if they are _real_ playbackdevices
mixer: only list playbackdevices if they are _real_ playbackdevices

tizenorg/platform.upstream.enlightenment,tasn/enlightenment,rvandegrift/e,rvandegrift/e,rvandegrift/e,tasn/enlightenment,tasn/enlightenment,tizenorg/platform.upstream.enlightenment,tizenorg/platform.upstream.enlightenment