correct documentation for ast_sched_add (bug #4136)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5556 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/sched.h

@@ -62,7 +62,7 @@ typedef int (*ast_sched_cb)(void *data);
  * Schedule an event to take place at some point in the future.  callback 
  * will be called with data as the argument, when milliseconds into the
  * future (approximately)
- * Returns 0 on success, -1 on failure
+ * Returns a schedule item ID on success, -1 on failure
  */
 extern int ast_sched_add(struct sched_context *con, int when, ast_sched_cb callback, void *data);