drm/exynos: g2d: make ioctls more robust

Both exynos_g2d_set_cmdlist_ioctl and exynos_g2d_exec_ioctl don't check
if the G2D was succesfully probe. If that is not the case, then g2d_priv
is just NULL and extracting 'dev' from it in the next step  is going to
produce a kernel oops.

Add proper checks and return ENODEV if the G2D is not available.
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: INki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -1056,7 +1056,7 @@ int exynos_g2d_set_cmdlist_ioctl(struct drm_device *drm_dev, void *data,
 {
 	struct drm_exynos_file_private *file_priv = file->driver_priv;
 	struct exynos_drm_g2d_private *g2d_priv = file_priv->g2d_priv;
-	struct device *dev = g2d_priv->dev;
+	struct device *dev;
 	struct g2d_data *g2d;
 	struct drm_exynos_g2d_set_cmdlist *req = data;
 	struct drm_exynos_g2d_cmd *cmd;
@@ -1067,6 +1067,10 @@ int exynos_g2d_set_cmdlist_ioctl(struct drm_device *drm_dev, void *data,
 	int size;
 	int ret;
 
+	if (!g2d_priv)
+		return -ENODEV;
+
+	dev = g2d_priv->dev;
 	if (!dev)
 		return -ENODEV;
 
@@ -1223,13 +1227,17 @@ int exynos_g2d_exec_ioctl(struct drm_device *drm_dev, void *data,
 {
 	struct drm_exynos_file_private *file_priv = file->driver_priv;
 	struct exynos_drm_g2d_private *g2d_priv = file_priv->g2d_priv;
-	struct device *dev = g2d_priv->dev;
+	struct device *dev;
 	struct g2d_data *g2d;
 	struct drm_exynos_g2d_exec *req = data;
 	struct g2d_runqueue_node *runqueue_node;
 	struct list_head *run_cmdlist;
 	struct list_head *event_list;
 
+	if (!g2d_priv)
+		return -ENODEV;
+
+	dev = g2d_priv->dev;
 	if (!dev)
 		return -ENODEV;