CRAS: audio_thread - Set sleep frames from fill function.
CRAS: audio_thread - Set sleep frames from fill function.

Similar to capture, set the sleep frame count in possibly_fill_audio.
This will allow for choosing the lower of the two delays (capture and
playback) in a later change.

BUG=247160
TEST=audio_thread_unittest still passes.

Change-Id: I4ae8fa3eda16aeee38edfd136fa6b881079e056c
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/60230
Reviewed-by: Chih-Chung Chang <ebe32a3bdce230d12f75781016b6b880113fb486@chromium.org>

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