sched/nohz: Fix logic in run_rebalance_domains
If triggered by nohz_balancer_kick, idle_at_tick is not updated
accordingly.  Update myself at this moment right before it is used

Change-Id: I20dd4314159e70f955ffe482160c8867c65c261e
Signed-off-by: Xin Qi <xqi@codeaurora.org>