wifi: rsi: fix kthread lifetime race between self-exit and external-stop

In the Linux kernel, the following vulnerability has been resolved: wifi: rsi: fix kthread lifetime race between self-exit and external-stop RSI driver use both self-exit(kthread_complete_and_exit) and external-stop (kthread_stop) when killing a kthread. Generally, kthread_stop() is called first, and in this case, no particular issues occur. However, in rare instances where kthread_complete_and_exit() is called first and then kthread_stop() is called, a UAF occurs because the kthread object, which has already exited and been freed, is accessed again. Therefore, to prevent this with minimal modification, you must remove kthread_stop() and change the code to wait until the self-exit operation is completed.