exit/rtl8712: Replace the macro thread_exit with a simple return 0

The macro thread_exit is called is at the end of a function 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 the cmd_thread return instead of calling complete_and_exit.

Link: https://lkml.kernel.org/r/20211020174406.17889-19-ebiederm@xmission.comSigned-off-by: Eric W. Biederman <ebiederm@xmission.com>

drivers/staging/rtl8712/osdep_service.h

@@ -37,7 +37,6 @@ struct	__queue	{
 
 #define _pkt struct sk_buff
 #define _buffer unsigned char
-#define thread_exit() complete_and_exit(NULL, 0)
 
 #define _init_queue(pqueue)				\
 	do {						\

drivers/staging/rtl8712/rtl8712_cmd.c

@@ -393,7 +393,7 @@ int r8712_cmd_thread(void *context)
 		r8712_free_cmd_obj(pcmd);
 	} while (1);
 	complete(&pcmdpriv->terminate_cmdthread_comp);
-	thread_exit();
+	return 0;
 }
 
 void r8712_event_handle(struct _adapter *padapter, __le32 *peventbuf)