adler32: Fix doxy group definition

Based on a patch by James Almer <jamrial@gmail.com>.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavutil/adler32.c

@@ -21,6 +21,15 @@
  * 3. This notice may not be removed or altered from any source distribution.
  */
 
+/**
+ * @file
+ * Computes the Adler-32 checksum of a data stream
+ *
+ * This is a modified version based on adler32.c from the zlib library.
+ * @author Mark Adler
+ * @ingroup lavu_adler32
+ */
+
 #include "config.h"
 #include "adler32.h"
 

libavutil/adler32.h

@@ -25,7 +25,15 @@
 #include "attributes.h"
 
 /**
+ * @file
+ * Public header for libavutil Adler32 hasher
+ *
+ * @defgroup lavu_adler32 Adler32
  * @ingroup lavu_crypto
+ * @{
+ */
+
+/**
  * Calculate the Adler32 checksum of a buffer.
  *
  * Passing the return value to a subsequent av_adler32_update() call
@@ -40,4 +48,8 @@
 unsigned long av_adler32_update(unsigned long adler, const uint8_t *buf,
                                 unsigned int len) av_pure;
 
+/**
+ * @}
+ */
+
 #endif /* AVUTIL_ADLER32_H */