Fix bug in CallManager unregisterForPhoneStates()

In this function, it asserts the handler pointer by mistake,
so it should stop&release related resources but actually not.
Therefore, when the Phone instance is registerred again, it
will hit mess due to old resources are not cleared. One example
of issue is for IMS Phone: when enter/exit flight mode, IMS
Phone instance will be unregistered and registered again, but
IMS phone registration will fail due to this bug, thus blocks IMS
functions.

Change-Id: I84ff4dcdddf6a8b0d52b5f3bec4ced008cc79fe3
Signed-off-by: chao.bi <chao.bi@intel.com>
Signed-off-by: Zhiquan Liu <zhiquan.liu@intel.com>