cpufreq_stats: fix to process policy exit in notifier

In the cpufreq framework before issuing notifier call with
policy exit event policy table is made NULL and cpufreq stat
driver policy notifier function is being called for policy
exit event, in the notifier call policy table is retrieved
before proceding with the policy exit event as cpufreq FW
marked policy table as NULL, notifier call returns without
processing policy exit events.

Moving policy exit event handling prior to policy table NULL check to
address this issue.

CRs-Fixed: 1093951
Change-Id: I9540ce8089c4035c13f7ffa8522d4a179657a254
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>