USB: fix build error in drivers/usb/serial/console.c

Thanks to Adrian Bunk <bunk@fs.tum.de> for pointing this out.

drivers/usb/serial/console.c

@@ -137,7 +137,7 @@ static int __init usb_console_setup(struct console *co, char *options)
 
 	/* grab the first serial port that happens to be connected */
 	serial = usb_serial_get_by_index(0);
-	if (serial_paranoia_check (serial, __FUNCTION__)) {
+	if (serial == NULL) {
 		/* no device is connected yet, sorry :( */
 		err ("No USB device connected to ttyUSB0");
 		return -ENODEV;