Fix typo(s) in comment(s) in the scheduling system.

First one:

   if (diff < sched_run_interval) {
     next_run.tv_sec = 0;
     /* Takes 1000 ms -> us. This will always be valid because diff can NOT be
-     * negative and can NOT be smaller than sched_run_interval so values can
+     * negative and can NOT be bigger than sched_run_interval so values can

There's no way there isn't more, so I'm making this a generalized ticket.