Sync SDL2 wiki -> header

include/SDL_audio.h

@@ -154,6 +154,7 @@ typedef Uint16 SDL_AudioFormat;
  * \param userdata An application-specific parameter saved in the
  *                 SDL_AudioSpec structure
  * \param stream A pointer to the audio data buffer.
+ * \param len Length of **stream** in bytes.
  */
 typedef void (SDLCALL * SDL_AudioCallback) (void *userdata, Uint8 * stream,
                                             int len);