drm/exynos: fix missed calling of drm_prime_gem_destroy()

When obj->import_attach is existed, code calling drm_prime_gem_destroy()
was removed from commit 67e93c808b48 ("drm/exynos: stop copying sg
table"), and it's a fault.

The drm_prime_gem_destroy() is cleanup function which GEM drivers need
to call when they use drm_gem_prime_import() to import dma-bufs, so
exynos-drm driver using drm_gem_prime_import() needs calling
drm_prime_gem_destroy().

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index a4fb78e..ce05f13 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -157,11 +157,10 @@
 	 * once dmabuf's refcount becomes 0.
 	 */
 	if (obj->import_attach)
-		goto out;
+		drm_prime_gem_destroy(obj, exynos_gem_obj->sgt);
+	else
+		exynos_drm_free_buf(exynos_gem_obj);
 
-	exynos_drm_free_buf(exynos_gem_obj);
-
-out:
 	drm_gem_free_mmap_offset(obj);
 
 	/* release file pointer to gem object. */
@@ -589,6 +588,8 @@
 	if (ret < 0)
 		goto err_free_large;
 
+	exynos_gem_obj->sgt = sgt;
+
 	if (sgt->nents == 1) {
 		/* always physically continuous memory if sgt->nents is 1. */
 		exynos_gem_obj->flags |= EXYNOS_BO_CONTIG;