exit/r8188eu: Replace the macro thread_exit with a simple return 0

The macro thread_exit is called is at the end of functions started
with kthread_run.  The code in kthread_run has arranged things so a
kernel thread can just return and do_exit will be called.

So just have rtw_cmd_thread and mp_xmit_packet_thread return instead
of calling complete_and_exit.

Link: https://lkml.kernel.org/r/20211020174406.17889-20-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

drivers/staging/r8188eu/core/rtw_cmd.c

@@ -347,7 +347,7 @@ post_process:
 
 	up(&pcmdpriv->terminate_cmdthread_sema);
 
-	thread_exit();
+	return 0;
 }
 
 u8 rtw_setstandby_cmd(struct adapter *padapter, uint action)

drivers/staging/r8188eu/core/rtw_mp.c

@@ -580,7 +580,7 @@ exit:
 	pmptx->pallocated_buf = NULL;
 	pmptx->stop = 1;
 
-	thread_exit();
+	return 0;
 }
 
 void fill_txdesc_for_mp(struct adapter *padapter, struct tx_desc *ptxdesc)

drivers/staging/r8188eu/include/osdep_service.h

@@ -49,8 +49,6 @@ struct	__queue	{
 	spinlock_t lock;
 };
 
-#define thread_exit() complete_and_exit(NULL, 0)
-
 static inline struct list_head *get_list_head(struct __queue *queue)
 {
 	return (&(queue->queue));