USB: g_printer: fix bug in unregistration

The allocated chardevice region range is only 1 device but on
unregister it currently tries to deregister 2.

Found this while doing a insmod/rmmod/insmod/rm... of the module
which seemed to eat major numbers.
Signed-off-by: NFabian Godehardt <fg@emlix.com>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/printer.c

@@ -1594,7 +1594,7 @@ cleanup(void)
 	if (status)
 		ERROR(dev, "usb_gadget_unregister_driver %x\n", status);
 
-	unregister_chrdev_region(g_printer_devno, 2);
+	unregister_chrdev_region(g_printer_devno, 1);
 	class_destroy(usb_gadget_class);
 	mutex_unlock(&usb_printer_gadget.lock_printer_io);
 }