drm/sun4i: Check return value of drm_vblank_init

drm_vblank_init can fail due to insufficient memory. Ignoring the error
and proceeding may cause the kernel to dereference an invalid pointer
when vblank is enabled.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

drivers/gpu/drm/sun4i/sun4i_drv.c

@@ -102,7 +102,11 @@ static int sun4i_drv_bind(struct device *dev)
 	}
 	drm->dev_private = drv;
 
-	drm_vblank_init(drm, 1);
+	/* drm_vblank_init calls kcalloc, which can fail */
+	ret = drm_vblank_init(drm, 1);
+	if (ret)
+		goto free_drm;
+
 	drm_mode_config_init(drm);
 
 	ret = component_bind_all(drm->dev, drm);