Prevent A2DP bit pool calculation endless loops.

This prevents log spam and endless loops in the A2DP bit pool
calculation. Protecting against the endless loop with prevent battery
draining issues and phone unresponsiveness.

This patch addresses the symptom. A separate patch will be submitted
once root cause is determined to address the problem.

Change-Id: I045b724c1c1638551b9333249f39eee109fa9ba1