staging: rtl8723bs: Remove set but not used variable 'adapter'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/staging/rtl8723bs/core/rtw_mlme.c: In function rtw_select_roaming_candidate:
drivers/staging/rtl8723bs/core/rtw_mlme.c:2007:18: warning: variable adapter set but not used [-Wunused-but-set-variable]

It is not used since commit 554c0a3a ("staging:
Add rtl8723bs sdio wifi driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1570352999-45790-6-git-send-email-zhengbin13@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_mlme.c

@@ -1989,7 +1989,6 @@ int rtw_select_roaming_candidate(struct mlme_priv *mlme)
 {
 	int ret = _FAIL;
 	struct list_head	*phead;
-	struct adapter *adapter;
 	struct __queue	*queue	= &(mlme->scanned_queue);
 	struct	wlan_network	*pnetwork = NULL;
 	struct	wlan_network	*candidate = NULL;
@@ -2001,7 +2000,6 @@ int rtw_select_roaming_candidate(struct mlme_priv *mlme)
 
 	spin_lock_bh(&(mlme->scanned_queue.lock));
 	phead = get_list_head(queue);
-	adapter = (struct adapter *)mlme->nic_hdl;
 
 	mlme->pscanned = get_next(phead);