drm/exynos: g2d: fix null pointer dereference

This patch fixes a null pointer dereference issue incurred by
calling g2d_remove when exynos_drm_platform_probe is failed.

cmdlist_pool of g2d is allocated when g2d sub driver is probed.
So if exynos_drm_platform_probe is failed, the g2d sub driver is
not probed and the cmdlist_pool is still NULL.
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -302,9 +302,12 @@ static void g2d_fini_cmdlist(struct g2d_data *g2d)
 	struct exynos_drm_subdrv *subdrv = &g2d->subdrv;
 
 	kfree(g2d->cmdlist_node);
-	dma_free_attrs(subdrv->drm_dev->dev, G2D_CMDLIST_POOL_SIZE,
-			g2d->cmdlist_pool_virt,
-			g2d->cmdlist_pool, &g2d->cmdlist_dma_attrs);
+
+	if (g2d->cmdlist_pool_virt && g2d->cmdlist_pool) {
+		dma_free_attrs(subdrv->drm_dev->dev, G2D_CMDLIST_POOL_SIZE,
+				g2d->cmdlist_pool_virt,
+				g2d->cmdlist_pool, &g2d->cmdlist_dma_attrs);
+	}
 }
 
 static struct g2d_cmdlist_node *g2d_get_cmdlist(struct g2d_data *g2d)