CRAS: audio_thread - modify initial callback time for new streams

Using next callback time of first stream may cause underrun. We need to
use earliest instead.

BUG=chromium:865338
TEST=I wrote a script to create new streams with different buffer size. It
causes underrun in previous version. The bug is fixed in this change.

Change-Id: Iad5f1d492a6043ef993ffbe98ae575065d1ffefa
Reviewed-on: https://chromium-review.googlesource.com/1143165
Commit-Ready: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
1 file changed