In clocksource_enqueue(), it is unnecessary to continue looping
the list, if we find there is an entry that the value of rating
is smaller than the new one. It is safe to be out the loop,
because all of entry are inserted in descending order.

Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: NMinfei Huang <mnghuan@gmail.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>