sched: run_rebalance_domains: s/SCHED_IDLE/CPU_IDLE/

rebalance_domains(SCHED_IDLE) looks strange (typo), change it to CPU_IDLE.

the effect of this bug was slightly more agressive idle-balancing on
SMP than intended.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Ingo Molnar <mingo@elte.hu>