bluetooth: poll GetBluezSinkHFPDevice

Poll the GetBluezSinkHFPDevice in StartPlayingAudioSubprocess to
make it more stable.

BUG=b:191722792
TEST=test_that bluetooth_AdapterAUHealth. \
        au_hfp_wbs_dut_as_source_back2back_test

Change-Id: Iada1fba0300d0cc5e4422a707358bc459b9cdba8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/chameleon/+/3622994
Tested-by: John Lai <johnlai@google.com>
Reviewed-by: Shyh-In Hwang <josephsih@chromium.org>
Commit-Queue: John Lai <johnlai@google.com>
Auto-Submit: John Lai <johnlai@google.com>
1 file changed