alsa_sound: Fix for voice volume restore after reboot

  - Maximum volume is heard for call after reboot even if it
    was set to minimum during the last call before reboot.

  - During call after reboot, mLastvoiceVolume is getting
    updated improperly and hence proper volume is not
    being applied.

  - Fix is to cache the voice Volume properly.

  CRs-Fixed: 517731

Change-Id: Ia9512afaab94407f04011541db1b49b41cd5707a