brcm80211: fmac: make sure cancel_work_sync only called after INIT_WORK

INIT_WORK only gets called after brcmf_proto_attach returns
success. This dependency should be annotated in brcmf_detach to
avoid any error.
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Franky Lin <frankyl@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

@@ -1109,13 +1109,13 @@ void brcmf_detach(struct device *dev)
 		if (drvr->iflist[i])
 			brcmf_del_if(drvr, i);
 
-	cancel_work_sync(&drvr->setmacaddr_work);
-	cancel_work_sync(&drvr->multicast_work);
-
 	brcmf_bus_detach(drvr);
 
-	if (drvr->prot)
+	if (drvr->prot) {
+		cancel_work_sync(&drvr->setmacaddr_work);
+		cancel_work_sync(&drvr->multicast_work);
 		brcmf_proto_detach(drvr);
+	}
 
 	bus_if->drvr = NULL;
 	kfree(drvr);