audio: calculate mute duration using getOutputLatency

-AudioSource mutes for predefined duration
 (kAutoRampStartUs)  at the beginning of a recording.
 Since kAutoRampStartUs is zero, video recording tone
 is also getting recorded in the beggining.

-Fix is to get the output latency of current playback
 stream from audio system to calculate mute duration.

Change-Id: Ib9f4d38fcc8478d148719b70358644c581ba2f25
CRs-fixed: 615511