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 67e93c80 ("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>

drivers/gpu/drm/exynos/exynos_drm_gem.c

@@ -157,11 +157,10 @@ void exynos_drm_gem_destroy(struct exynos_drm_gem_obj *exynos_gem_obj)
 	 * 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);
 
-out:
 	drm_gem_free_mmap_offset(obj);
 
 	/* release file pointer to gem object. */
@@ -589,6 +588,8 @@ exynos_drm_gem_prime_import_sg_table(struct drm_device *dev,
 	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;

drivers/gpu/drm/exynos/exynos_drm_gem.h

@@ -39,6 +39,7 @@
  *	- this address could be physical address without IOMMU and
  *	device address with IOMMU.
  * @pages: Array of backing pages.
+ * @sgt: Imported sg_table.
  *
  * P.S. this object would be transferred to user as kms_bo.handle so
  *	user can access the buffer through kms_bo.handle.
@@ -52,6 +53,7 @@ struct exynos_drm_gem_obj {
 	dma_addr_t		dma_addr;
 	struct dma_attrs	dma_attrs;
 	struct page		**pages;
+	struct sg_table		*sgt;
 };
 
 struct page **exynos_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask);