stagefright: Fix SurfaceMediaSource buffer search condition when buffer return

Refer to commit 3e328782, buffer
handle stored in MediaBuffer had changed, but the buffer return
code did not change correspondingly, so returned buffer can't be
found in list and lead to crash.

This commit fix it and make wifidisplay working now.

Change-Id: Ic0d99f471f5f246087946367726d7e76a689fe1f