USB: serial: symbolserial: simplify endpoint check

Simplify the endpoint sanity check by letting core verify that the
required endpoints are present.
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/symbolserial.c

@@ -147,16 +147,6 @@ static void symbol_unthrottle(struct tty_struct *tty)
 	}
 }
 
-static int symbol_startup(struct usb_serial *serial)
-{
-	if (!serial->num_interrupt_in) {
-		dev_err(&serial->dev->dev, "no interrupt-in endpoint\n");
-		return -ENODEV;
-	}
-
-	return 0;
-}
-
 static int symbol_port_probe(struct usb_serial_port *port)
 {
 	struct symbol_private *priv;
@@ -188,7 +178,7 @@ static struct usb_serial_driver symbol_device = {
 	},
 	.id_table =		id_table,
 	.num_ports =		1,
-	.attach =		symbol_startup,
+	.num_interrupt_in =	1,
 	.port_probe =		symbol_port_probe,
 	.port_remove =		symbol_port_remove,
 	.open =			symbol_open,