Clarify doxy for av_fifo_alloc().

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@22812 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavutil/fifo.h

@@ -35,7 +35,7 @@ typedef struct AVFifoBuffer {
 /**
  * Initializes an AVFifoBuffer.
  * @param size of FIFO
- * @return AVFifoBuffer or NULL if mem allocation failure
+ * @return AVFifoBuffer or NULL in case of memory allocation failure
  */
 AVFifoBuffer *av_fifo_alloc(unsigned int size);