timer: fix misleading comment in timer.h

It's timer to expire, not clock.

Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Message-Id: <1480566640-27264-1-git-send-email-baiyaowei@cmss.chinamobile.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/timer.h

@@ -133,7 +133,7 @@ bool qemu_clock_has_timers(QEMUClockType type);
  * @type: the clock type
  *
  * Determines whether a clock's default timer list
- * has an expired clock.
+ * has an expired timer.
  *
  * Returns: true if the clock's default timer list has
  * an expired timer