avutil/lfg: Add doxy for missing argument

libavutil/lfg.h

@@ -73,6 +73,7 @@ static inline unsigned int av_mlfg_get(AVLFG *c){
  * Get the next two numbers generated by a Box-Muller Gaussian
  * generator using the random numbers issued by lfg.
  *
+ * @param lfg pointer to the contex structure
  * @param out array where the two generated numbers are placed
  */
 void av_bmg_get(AVLFG *lfg, double out[2]);