rtl8xxxu: Do not overwrite rtl8xxxu_debug for untested chips

Fix a silly bug where the debug level was overwritten rather than
amended for untested chips.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu.c

@@ -6391,7 +6391,7 @@ static int rtl8xxxu_probe(struct usb_interface *interface,
 	}
 
 	if (untested) {
-		rtl8xxxu_debug = RTL8XXXU_DEBUG_EFUSE;
+		rtl8xxxu_debug |= RTL8XXXU_DEBUG_EFUSE;
 		dev_info(&udev->dev,
 			 "This Realtek USB WiFi dongle (0x%04x:0x%04x) is untested!\n",
 			 id->idVendor, id->idProduct);