staging: rtl8188eu: use safe iterator in tx_beacon_hdl()

This loop calls list_del_init() on the list iterator so it has to use
the _safe() iterator or it leads to an endless loop.

Fixes: 23017c88 ("staging: rtl8188eu: Use list iterators and helpers")
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YL5iunD5ilf+mKPR@mwandaSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_mlme_ext.c

@@ -5376,8 +5376,8 @@ u8 tx_beacon_hdl(struct adapter *padapter, unsigned char *pbuf)
 #ifdef CONFIG_88EU_AP_MODE
 	else { /* tx bc/mc frames after update TIM */
 		struct sta_info *psta_bmc;
-		struct list_head *xmitframe_plist, *xmitframe_phead;
-		struct xmit_frame *pxmitframe = NULL;
+		struct list_head *xmitframe_phead;
+		struct xmit_frame *pxmitframe, *n;
 		struct sta_priv *pstapriv = &padapter->stapriv;
 
 		/* for BC/MC Frames */
@@ -5390,11 +5390,8 @@ u8 tx_beacon_hdl(struct adapter *padapter, unsigned char *pbuf)
 			spin_lock_bh(&psta_bmc->sleep_q.lock);
 
 			xmitframe_phead = get_list_head(&psta_bmc->sleep_q);
-			list_for_each(xmitframe_plist, xmitframe_phead) {
-				pxmitframe = list_entry(xmitframe_plist,
-							struct xmit_frame,
-							list);
-
+			list_for_each_entry_safe(pxmitframe, n, xmitframe_phead,
+						 list) {
 				list_del_init(&pxmitframe->list);
 
 				psta_bmc->sleepq_len--;