Bluetooth: controller: Fix Conn Param Req response timeout

When the peer slave rejects a Connection Parameter Request
Procedure, the controller proceeds to perform a Connection
Update Procedure without clearing the procedure timer that
causes the connection to terminate eventually. This is
fixed by clearing the procedure timeout when the Connection
Update Procedure completes.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>