core_ctl: Update cluster->active_cpus in eval_need()

The cluster->active_cpus is not updated in eval_need(). The new need
for CPUs is compared against the previous cluster->active_cpus. If
another client isolates a CPU, cluster->active_cpus becomes stale and
we fail to detect the change in need for CPUs.

Change-Id: I657cd615d6658fe8574c026e2703dec18891b14a
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>