staging: rtl8723au: core: rtw_mlme: fix void function return statements

The following patch fixes the checkpatch.pl warning:

drivers/staging/rtl8723au/core/rtw_mlme.c WARNING: void function return statements are not generally useful
Signed-off-by: Yeliz Taneroglu <yeliztaneroglu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723au/core/rtw_mlme.c

@@ -218,8 +218,6 @@ void rtw_generate_random_ibss23a(u8 *pibss)
 	pibss[3] = curtime & 0xff;/* p[0]; */
 	pibss[4] = (curtime >> 8) & 0xff;/* p[1]; */
 	pibss[5] = (curtime >> 16) & 0xff;/* p[2]; */
-
-	return;
 }
 
 void rtw_set_roaming(struct rtw_adapter *adapter, u8 to_roaming)
@@ -579,8 +577,6 @@ void rtw_atimdone_event_callback23a(struct rtw_adapter *adapter, const u8 *pbuf)
 {
 	RT_TRACE(_module_rtl871x_mlme_c_, _drv_err_,
 		 ("receive atimdone_evet\n"));
-
-	return;
 }
 
 void rtw_survey_event_cb23a(struct rtw_adapter *adapter, const u8 *pbuf)
@@ -650,8 +646,6 @@ void rtw_survey_event_cb23a(struct rtw_adapter *adapter, const u8 *pbuf)
 
 	kfree(survey->bss);
 	survey->bss = NULL;
-
-	return;
 }
 
 void