nuplayer: update anchor time for offload usecase

   In non-offload usecase, mAnchorTmeMediaUs is updated
   for every audio FillBufferDone. Added the same logic
   for offload case, otherwise  video updates max media
   duration as ZERO, for clips which have small audio
   data, and all the buffers are sent to DSP before first
   video buffer is processed at NuPlayerRenderer level

Change-Id: Ib6e0f251207c87ad1525041d07187cef91f4dda5