Make sure the description of pause() is

equivalent to its implementation.
No code change.

Suggested by:	Bruce Evans
MFC after:	3 days

sys/kern/kern_synch.c

@@ -328,7 +328,8 @@ msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
  * pause() delays the calling thread by the given number of system ticks.
  * During cold bootup, pause() uses the DELAY() function instead of
  * the tsleep() function to do the waiting. The "timo" argument must be
- * greater than zero.
+ * greater than or equal to zero. A "timo" value of zero is equivalent
+ * to a "timo" value of one.
  */
 int
 pause(const char *wmesg, int timo)