libstagefright: call release encoder instead of signalEOS

In SignalEOS(), it releases encoder and calls
puller stop source, Meanwhile if camera was shutdown
and puller read was bolcked, StopSource will never
get execute and gets blocked. To avoid the same,
release only encoder, this will handle timed out
issue in camera source reset.

Change-Id: Id75055e85fad3f6802f9939c7536fa8ce00dcb43