brcmfmac: fix invalid ifp lookup in firmware-signalling

The destination entries for firmware-signalled flow control have
the interface id stored. This needs to be translated to bsscfg
index when looking up the ifp object for the interface.
Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -805,7 +805,7 @@ static void
 brcmf_fws_flow_control_check(struct brcmf_fws_info *fws, struct pktq *pq,
 			     u8 if_id)
 {
-	struct brcmf_if *ifp = fws->drvr->iflist[if_id];
+	struct brcmf_if *ifp = fws->drvr->iflist[!if_id ? 0 : if_id + 1];
 
 	if (WARN_ON(!ifp))
 		return;