Duplicate pair request are generated in BLE SMP.

SMP_SEC_REQUEST_EVT  will trigger pair request for user permission.
Due to callback event isn't cleared, duplicate pare request is generated.
The fix is to clear the callback event after grant the permission for the pair request.
To avoid reporting duplicae SMP_SEC_REQUEST_EVT.

bug:11716879
Change-Id: I90805caa6f5360f8d64edfb711703e0e05863ea4