acer-wmi: set permissions on interface file to S_IRUGO

The interface file is not writable, thus set permissions to S_IRUGO.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/acer-wmi.c

@@ -1084,8 +1084,7 @@ static ssize_t show_interface(struct device *dev, struct device_attribute *attr,
 	}
 }
 
-static DEVICE_ATTR(interface, S_IWUGO | S_IRUGO | S_IWUSR,
-	show_interface, NULL);
+static DEVICE_ATTR(interface, S_IRUGO, show_interface, NULL);
 
 /*
  * debugfs functions