drm/i915: use kobj_to_dev()

Use kobj_to_dev() instead of open-coding it.
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/f5db8b56cd177972c901d01aa87ba763735438a9.1452696179.git.geliangtang@163.com

drivers/gpu/drm/i915/i915_sysfs.c

@@ -164,7 +164,7 @@ i915_l3_read(struct file *filp, struct kobject *kobj,
 	     struct bin_attribute *attr, char *buf,
 	     loff_t offset, size_t count)
 {
-	struct device *dev = container_of(kobj, struct device, kobj);
+	struct device *dev = kobj_to_dev(kobj);
 	struct drm_minor *dminor = dev_to_drm_minor(dev);
 	struct drm_device *drm_dev = dminor->dev;
 	struct drm_i915_private *dev_priv = drm_dev->dev_private;
@@ -200,7 +200,7 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
 	      struct bin_attribute *attr, char *buf,
 	      loff_t offset, size_t count)
 {
-	struct device *dev = container_of(kobj, struct device, kobj);
+	struct device *dev = kobj_to_dev(kobj);
 	struct drm_minor *dminor = dev_to_drm_minor(dev);
 	struct drm_device *drm_dev = dminor->dev;
 	struct drm_i915_private *dev_priv = drm_dev->dev_private;
@@ -521,7 +521,7 @@ static ssize_t error_state_read(struct file *filp, struct kobject *kobj,
 				loff_t off, size_t count)
 {
 
-	struct device *kdev = container_of(kobj, struct device, kobj);
+	struct device *kdev = kobj_to_dev(kobj);
 	struct drm_minor *minor = dev_to_drm_minor(kdev);
 	struct drm_device *dev = minor->dev;
 	struct i915_error_state_file_priv error_priv;
@@ -556,7 +556,7 @@ static ssize_t error_state_write(struct file *file, struct kobject *kobj,
 				 struct bin_attribute *attr, char *buf,
 				 loff_t off, size_t count)
 {
-	struct device *kdev = container_of(kobj, struct device, kobj);
+	struct device *kdev = kobj_to_dev(kobj);
 	struct drm_minor *minor = dev_to_drm_minor(kdev);
 	struct drm_device *dev = minor->dev;
 	int ret;