Conditional compilation for 48KHz sample rate

Summary: Change-Id: I901e83dac9e18343dad4fad9c6ebf5f58c24ebf5

Test Plan:
need to confirm functionality, anybody know how how to
           test a2dp sample rate?

Reviewers: synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D406