[autotest] audio_helper: Fix cross-correlatino best delay computation

The computation of best delay should take the length of data being
trimmed in the end into consideration instead of the length of data
being trimmed in the front.

BUG=chromium:512320
TEST=run audio_AudioBasicHDMI test on link.
Signed-off-by: Cheng-Yi Chiang <cychiang@chromium.org>

Change-Id: I90a97627076abd8eb0cdafccac47bd36ed0cbda6
Reviewed-on: https://chromium-review.googlesource.com/292640
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed