brcmfmac: Check null pointer on brcmf_dev_reset.

When unloading it is possible that drvr is not null, but iflist[0]
is. So check iflist[0] pointer before using it.
Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Piotr Haber <phaber@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/dhd_linux.c

@@ -842,7 +842,8 @@ void brcmf_dev_reset(struct device *dev)
 	if (drvr == NULL)
 		return;
 
-	brcmf_fil_cmd_int_set(drvr->iflist[0], BRCMF_C_TERMINATED, 1);
+	if (drvr->iflist[0])
+		brcmf_fil_cmd_int_set(drvr->iflist[0], BRCMF_C_TERMINATED, 1);
 }
 
 void brcmf_detach(struct device *dev)