brcmfmac: fix potential NULL pointer dereference in brcmf_fws_flow_control_check()

The dereference to 'ifp' in debug code should be moved below the NULL test.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/brcm80211/brcmfmac/fwsignal.c

@@ -834,11 +834,12 @@ brcmf_fws_flow_control_check(struct brcmf_fws_info *fws, struct pktq *pq,
 {
 	struct brcmf_if *ifp = fws->drvr->iflist[if_id];
 
-	brcmf_dbg(TRACE,
-		  "enter: bssidx=%d, ifidx=%d\n", ifp->bssidx, ifp->ifidx);
 	if (WARN_ON(!ifp))
 		return;
 
+	brcmf_dbg(TRACE,
+		  "enter: bssidx=%d, ifidx=%d\n", ifp->bssidx, ifp->ifidx);
+
 	if ((ifp->netif_stop & BRCMF_NETIF_STOP_REASON_FWS_FC) &&
 	    pq->len <= BRCMF_FWS_FLOWCONTROL_LOWATER)
 		brcmf_txflowblock_if(ifp,