Bluetooth: Validate HCI device handle before updating scan state

Check if the HCI device handle is available prior to updating
the scan state.

Signed-off-by: Anantha Krishnan <ananthk@codeaurora.org>

CRs-fixed: 447893

Change-Id: Ifc278afecbcf2bc7a95bb6595028dd890a8b60f5
Signed-off-by: Fujun Wu <fujunw@codeaurora.org>