qcacld-3.0: deregister policy mgr cb upon stop modules

There is chance that some active thread is running and
skip stop modules. In that case driver should not
deregister policy mgr callback.
Call hdd_deregister_policy_manager_callback after
active thread check when stop modules.

Change-Id: I5fe3e438e87da0b333ae9b20994e58228fa67918
CRs-Fixed: 2443271