audio: Increased mute wait for USB Playback

- Sometimes, when touch tones are played over USB Headset
  glitch is heard. This issue is seen when startOuput
  is called for touch tone after the device goes into
  standby

- Fix is to increase the mute wait during starting of the
  output to give additional time for the proxy device to
  come up

CRs-Fixed: 615405

Change-Id: I37b772582058ec6939ca13067a31360a4de9784b