nuplayer: Fix max buffer size for audio only streaming playback

Currently, audio only streaming playback with very low frame size
faces underrun in compressed playback. This causes underruns while
playing initial frames. By increasing the max buffer accumulation
limit in Generic source, the underrun is avoided.

Change-Id: I37949f65b9a08d0776f2346d665399be2ecd0265
CRs-Fixed: 875129