drm/sysfs: use kobj_to_dev()

BugLink: http://bugs.launchpad.net/bugs/1546572

Use kobj_to_dev() instead of open-coding it.

Link: http://patchwork.freedesktop.org/patch/msgid/3fea991541fbfc4ffece2c174adeb02cb9436c90.1452696179.git.geliangtang@163.comSigned-off-by: Geliang Tang <geliangtang@163.com>
(cherry picked from commit d122cbf1)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/drm_sysfs.c

@@ -252,7 +252,7 @@ static ssize_t edid_show(struct file *filp, struct kobject *kobj,
 			 struct bin_attribute *attr, char *buf, loff_t off,
 			 size_t count)
 {
-	struct device *connector_dev = container_of(kobj, struct device, kobj);
+	struct device *connector_dev = kobj_to_dev(kobj);
 	struct drm_connector *connector = to_drm_connector(connector_dev);
 	unsigned char *edid;
 	size_t size;