sched: Limit LBF_PWR_ACTIVE_BALANCE to within cluster

When higher power (performance) cluster has only one online cpu, we
currently let an idle cpu in lower power cluster pull a running task
from performance cluster via active balance. Active balance for
power-aware reasons is supposed to be restricted to balance within
cluster, the check for which is not correctly implemented.

Change-Id: I5fba7f01ad80c082a9b27e89b7f6b17a6d9cde14
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>