thunderbolt: Make key root-only accessible

Non-root user may read the key back after root wrote it there.
This removes read access to everyone but root.

Signed-off-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/switch.c

@@ -826,7 +826,7 @@ static ssize_t key_store(struct device *dev, struct device_attribute *attr,
 	mutex_unlock(&switch_lock);
 	return ret;
 }
-static DEVICE_ATTR_RW(key);
+static DEVICE_ATTR(key, 0600, key_show, key_store);
 
 static ssize_t nvm_authenticate_show(struct device *dev,
 	struct device_attribute *attr, char *buf)