staging: rtl8723bs: Fix possible usage of NULL pointer in core/rtw_debug.c

Smatch reports the following:

  CHECK   drivers/staging/rtl8723bs/core/rtw_debug.c
drivers/staging/rtl8723bs/core/rtw_debug.c:454 proc_get_survey_info() error: we previously assumed 'phead' could be null (see line 453)
drivers/staging/rtl8723bs/core/rtw_debug.c:455 proc_get_survey_info() warn: variable dereferenced before check 'phead' (see line 454)

In the code, there are two successive calls to get_head(). The second
is removed.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_debug.c

@@ -451,7 +451,6 @@ int proc_get_survey_info(struct seq_file *m, void *v)
 	spin_lock_bh(&(pmlmepriv->scanned_queue.lock));
 	phead = get_list_head(queue);
 	plist = phead ? get_next(phead) : NULL;
-	plist = get_next(phead);
 	if ((!phead) || (!plist)) {
 		spin_unlock_bh(&(pmlmepriv->scanned_queue.lock));
 		return 0;