Fix audio loop for long-delay keyboard reads.

BUG=chrome-os-partner:7428
TEST=manual

Switch to dev-mode, turn it on, see how long it takes.

With gbb.flags == 1 (factory mode), it should take 2 seconds.
(You'll see a warning on the screen if gbb.flags is nonzero)

With gbb.flags == 0 (after factory install), it should take 30 seconds.
You should hear two beeps at 20 seconds.

Change-Id: I4f14128b87d3482e291b1b40a11a6d27c72c1ad1
Reviewed-on: https://gerrit.chromium.org/gerrit/14534
Tested-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Commit-Ready: Bill Richardson <wfrichar@chromium.org>
4 files changed