AwesomePlayer: correct stream type for offload

canOffloadStream() function in stagefright utils forces the
stream type to AUDIO_STREAM_MUSIC when querying the audio policy
manager if a particular track is offloadable or not.
This causes MP3 ringtones to be offloaded which is not a validated use case.

The fix consists in using the actual stream type read from the AudioSink.

Bug: 11410937.
Change-Id: I44b8e033a8e785a79cdc291b142f80b5580bdc4d