sound: Set decimator volume to default in disable sequence

- setting it to zero causes mute mic in other use cases that don't
  explicitly set the decimator volume in their enable sequences

Change-Id: I8f84f631ac5275a948112a005993ede0f4070cae
Merge pull request #7 from CyanogenMod/cm-11.0

sound: Set decimator volume to default in disable sequence