isdn/bas_gigaset: fix a leak on failure path in gigaset_probe()

There is a lack of usb_put_dev(udev) on failure path in gigaset_probe().

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: NAlexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: NTilman Schmidt <tilman@imap.cc>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/bas-gigaset.c

@@ -2400,6 +2400,7 @@ static int gigaset_probe(struct usb_interface *interface,
 error:
 	freeurbs(cs);
 	usb_set_intfdata(interface, NULL);
+	usb_put_dev(udev);
 	gigaset_freecs(cs);
 	return rc;
 }