Remove nonsense @return Doxygen comment for void function.

Originally committed as revision 15756 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/celp_filters.h

@@ -79,8 +79,6 @@ int ff_celp_lp_synthesis_filter(
  * @param buffer_length amount of data to process
  * @param filter_length filter length (10 for 10th order LP filter)
  *
- * @return 1 if overflow occurred, 0 - otherwise
- *
  * @note Output buffer must contain 10 samples of past
  *       speech data before pointer.
  *