vol_sadd
vol_sadd(sc->sc_volume[WM8731_OP_SPKR].left, ZAUDIO_VOLUME_STRIDE);
vol_sadd(sc->sc_volume[WM8731_OP_SPKR].right, ZAUDIO_VOLUME_STRIDE);
vol_sadd(sc->sc_volume[WM8750_OP_SPKR].left, ZAUDIO_VOLUME_STRIDE);
vol_sadd(sc->sc_volume[WM8750_OP_HP].left, ZAUDIO_VOLUME_STRIDE);
vol_sadd(sc->sc_volume[WM8750_OP_HP].right, ZAUDIO_VOLUME_STRIDE);