brcmfmac: on halting driver check before release or free.

brcmf_netdev_stop shall first check bus_if status before bringing
down cfg80211. brcmf_detach shall first check if driver is
allocated.
Reviewed-by: NArend Van Spriel <arend@broadcom.com>
Signed-off-by: NHante Meuleman <meuleman@broadcom.com>
Signed-off-by: NFranky Lin <frankyl@broadcom.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -600,10 +600,12 @@ static int brcmf_netdev_stop(struct net_device *ndev)
 	struct brcmf_pub *drvr = ifp->drvr;
 
 	brcmf_dbg(TRACE, "Enter\n");
-	brcmf_cfg80211_down(drvr->config);
+
 	if (drvr->bus_if->drvr_up == 0)
 		return 0;
 
+	brcmf_cfg80211_down(drvr->config);
+
 	/* Set state and stop OS transmissions */
 	drvr->bus_if->drvr_up = false;
 	netif_stop_queue(ndev);
@@ -905,6 +907,8 @@ void brcmf_detach(struct device *dev)
 
 	brcmf_dbg(TRACE, "Enter\n");
 
+	if (drvr == NULL)
+		return;
 
 	/* make sure primary interface removed last */
 	for (i = BRCMF_MAX_IFS-1; i > -1; i--)