drm/exynos: g2d: let exynos_g2d_get_ver_ioctl fail

Currently the DRM_IOCTL_EXYNOS_G2D_GET_VER ioctl always succeeds, even
if no G2D support is available. Let the ioctl fail when this is the
case, so that userspace can accurately probe for G2D support.

This also fixes the exynos tests in libdrm. There 'g2d_init' doesn't
fail when G2D is absent, leading to a segfault later.
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

@@ -1042,8 +1042,23 @@ static int g2d_check_reg_offset(struct device *dev,
 int exynos_g2d_get_ver_ioctl(struct drm_device *drm_dev, void *data,
 			     struct drm_file *file)
 {
+	struct drm_exynos_file_private *file_priv = file->driver_priv;
+	struct exynos_drm_g2d_private *g2d_priv = file_priv->g2d_priv;
+	struct device *dev;
+	struct g2d_data *g2d;
 	struct drm_exynos_g2d_get_ver *ver = data;
 
+	if (!g2d_priv)
+		return -ENODEV;
+
+	dev = g2d_priv->dev;
+	if (!dev)
+		return -ENODEV;
+
+	g2d = dev_get_drvdata(dev);
+	if (!g2d)
+		return -EFAULT;
+
 	ver->major = G2D_HW_MAJOR_VER;
 	ver->minor = G2D_HW_MINOR_VER;