dax: Simplify root read-only definition for the 'resource' attribute

Rather than update the permission in ->is_visible() set the permission
directly at declaration time.

Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Link: https://lore.kernel.org/r/157309904959.1582359.7281180042781955506.stgit@dwillia2-desk3.amr.corp.intel.com

drivers/dax/bus.c

@@ -309,7 +309,7 @@ static ssize_t resource_show(struct device *dev,
 
 	return sprintf(buf, "%#llx\n", dev_dax_resource(dev_dax));
 }
-static DEVICE_ATTR_RO(resource);
+static DEVICE_ATTR(resource, 0400, resource_show, NULL);
 
 static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 		char *buf)
@@ -329,8 +329,6 @@ static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
 
 	if (a == &dev_attr_target_node.attr && dev_dax_target_node(dev_dax) < 0)
 		return 0;
-	if (a == &dev_attr_resource.attr)
-		return 0400;
 	return a->mode;
 }