ALSA: line6: Yet more cleanup of superfluous NULL checks

... in line6_disconnect() as well.

Tested-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 93cd4da..e8d5138 100644
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -579,18 +579,9 @@
 */
 void line6_disconnect(struct usb_interface *interface)
 {
-	struct usb_line6 *line6;
-	struct usb_device *usbdev;
-	int interface_number;
+	struct usb_line6 *line6 = usb_get_intfdata(interface);
+	struct usb_device *usbdev = interface_to_usbdev(interface);
 
-	if (interface == NULL)
-		return;
-	usbdev = interface_to_usbdev(interface);
-	if (usbdev == NULL)
-		return;
-
-	interface_number = interface->cur_altsetting->desc.bInterfaceNumber;
-	line6 = usb_get_intfdata(interface);
 	if (!line6)
 		return;