stagefright: Fix buffer handle retrieval in signalBufferReturned

In commit 3e328782 the stagefright code was restructured to fix
the logic for native handle source, but the change in the
function SurfaceMediaSource::signalBufferReturned was probably
missed.

Try to compare the media buffer handle also to the current native
buffer handle in this function when searching for correspondance.

Change-Id: I352293e525f75dde500ac8e71ee49209710030c3
Signed-off-by: DennySPb <dennyspb@gmail.com>