staging: rtl8188eu: remove return from void function

Remove return from a void function to clear a checkpatch warning.
WARNING: void function return statements are not generally useful
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_mlme.c

@@ -592,9 +592,7 @@ void rtw_survey_event_callback(struct adapter	*adapter, u8 *pbuf)
 	}
 
 exit:
-
 	spin_unlock_bh(&pmlmepriv->lock);
-	return;
 }
 
 void rtw_surveydone_event_callback(struct adapter	*adapter, u8 *pbuf)