stagefright: Fix audio codec fallthru

 * We shouldn't return an error from setAudioFormat unless it's
   really an error since fallthru is necessary.
 * We don't even need to do this, since the component name is
   checked before calling into mm-parser or FFMPEG.
 * Fixes Vorbis decoding after FFMPEG patch.

Change-Id: I4871c62044c6693e5698119dee3a10c20c26e2c7