legacy/alsa_sound: Fix for Music and FM volume concurrency.

- Call music volume and FM volume subsequently, as both use
STREAM_MUSIC, and change in one should get effective in other
application.
- Initialize FM volume to zero in Audio HAL. Store FM volume
even if FM is not active.

Change-Id: I29eb30f30a42dd2cac05fb8566e5f0725618df89