avutil/lfg: Minor doxy improvements

Use inline code for sizeof and use proper @return directive.

libavutil/lfg.h

@@ -27,7 +27,7 @@
 /**
  * Context structure for the Lagged Fibonacci PRNG.
  * The exact layout, types and content of this struct may change and should
- * not be accessed directly. Only its sizeof() is guaranteed to stay the same
+ * not be accessed directly. Only its `sizeof()` is guaranteed to stay the same
  * to allow easy instanciation.
  */
 typedef struct AVLFG {
@@ -40,7 +40,7 @@ void av_lfg_init(AVLFG *c, unsigned int seed);
 /**
  * Seed the state of the ALFG using binary data.
  *
- * Return value: 0 on success, negative value (AVERROR) on failure.
+ * @return 0 on success, negative value (AVERROR) on failure.
  */
 int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);