brcmfmac: add a check for the status of usb_register

usb_register() may fail, so let's check its status and issue an error
message if it fails.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/broadcom/brcm80211/brcmfmac/usb.c

@@ -1550,6 +1550,10 @@ void brcmf_usb_exit(void)
 
 void brcmf_usb_register(void)
 {
+	int ret;
+
 	brcmf_dbg(USB, "Enter\n");
-	usb_register(&brcmf_usbdrvr);
+	ret = usb_register(&brcmf_usbdrvr);
+	if (ret)
+		brcmf_err("usb_register failed %d\n", ret);
 }