audioflinger: do not use raw pointer for tracks

Commit 9da3d95 surfaced a problem caused by the use of a raw
pointer to a track in offload thread implementation.

Pointers to tracks should always be weak or strong pointers.

Bug: 11708529.
Change-Id: Ic48632532d186c9be8261f73cefdf824b9fbbd2b
2 files changed