audio_parser: renamed parameter "error" to "error_r"

It's a double pointer.

src/audio_parser.h

@@ -37,11 +37,12 @@ struct audio_format;
  *
  * @param dest the destination #audio_format struct
  * @param src the input string
- * @param error location to store the error occuring, or NULL to
+ * @param error_r location to store the error occuring, or NULL to
  * ignore errors
  * @return true on success
  */
 bool
-audio_format_parse(struct audio_format *dest, const char *src, GError **error);
+audio_format_parse(struct audio_format *dest, const char *src,
+		   GError **error_r);
 
 #endif