sysclk-lwla: Clean up open/closed state handling

sysclk-lwla: Clean up open/closed state handling

Use states SR_ST_ACTIVE and SR_ST_INACTIVE to indicate that the
device is open or closed, respectively. Do not use any of the
other state values. Improve the robustness of the open and close
methods in face of errors. Introduce a separate flag to indicate
that a running acquisition should be canceled.