at76c50x-usb: avoid double usb_put_dev() after downloading internal firmware in at76_probe()

There is no need in usb_put_dev() if at76_load_internal_fw() succeed.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/atmel/at76c50x-usb.c

@@ -2481,9 +2481,7 @@ static int at76_probe(struct usb_interface *interface,
 			dev_err(&interface->dev,
 				"error %d downloading internal firmware\n",
 				ret);
-			goto exit;
 		}
-		usb_put_dev(udev);
 		goto exit;
 	}