Fix documentation of the return value of avcodec_encode_video().

ripped out of a patch by Bitbreaker/METALVOTZE X bitbreaker ihlaid de Y

Originally committed as revision 16870 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -2858,7 +2858,7 @@ int avcodec_encode_audio(AVCodecContext *avctx, uint8_t *buf, int buf_size,
  * @param[in] buf_size the size of the output buffer in bytes
  * @param[in] pict the input picture to encode
  * @return On error a negative value is returned, on success zero or the number
- * of bytes used from the input buffer.
+ * of bytes used from the output buffer.
  */
 int avcodec_encode_video(AVCodecContext *avctx, uint8_t *buf, int buf_size,
                          const AVFrame *pict);