staging: rtl8723bs: core: remove set but not used 'listen_interval'

Fix the following gcc warning:

drivers/staging/rtl8723bs/core/rtw_mlme_ext.c:1173:18: warning: variable
‘listen_interval’ set but not used [-Wunused-but-set-variable]
  u16 capab_info, listen_interval;
                  ^~~~~~~~~~~~~~~
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200427032342.27211-6-yanaijie@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_mlme_ext.c

@@ -1169,7 +1169,7 @@ unsigned int OnAuthClient(struct adapter *padapter, union recv_frame *precv_fram
 
 unsigned int OnAssocReq(struct adapter *padapter, union recv_frame *precv_frame)
 {
-	u16 capab_info, listen_interval;
+	u16 capab_info;
 	struct rtw_ieee802_11_elems elems;
 	struct sta_info *pstat;
 	unsigned char 	reassoc, *p, *pos, *wpa_ie;
@@ -1215,8 +1215,6 @@ unsigned int OnAssocReq(struct adapter *padapter, union recv_frame *precv_frame)
 
 	capab_info = RTW_GET_LE16(pframe + WLAN_HDR_A3_LEN);
 	/* capab_info = le16_to_cpu(*(unsigned short *)(pframe + WLAN_HDR_A3_LEN)); */
-	/* listen_interval = le16_to_cpu(*(unsigned short *)(pframe + WLAN_HDR_A3_LEN+2)); */
-	listen_interval = RTW_GET_LE16(pframe + WLAN_HDR_A3_LEN+2);
 
 	left = pkt_len - (sizeof(struct ieee80211_hdr_3addr) + ie_offset);
 	pos = pframe + (sizeof(struct ieee80211_hdr_3addr) + ie_offset);