audioflinger: check for condition before waiting

AsyncCallbackThread must check for any condition that
was already been satisfied before waiting.

CRs-Fixed: 581978
Change-Id: I7a37c03cddcf7fdaa61c826d71a4d527979ce9e1
Increase kFastTrackMultiplier from 1 to 2

Change-Id: I158f147295eebcea96e4047d7618069bc48bdd7d