drm/exynos: check for null in return value of dma_buf_map_attachment()

dma_buf_map_attachment() can return NULL and valid sg as return
value. Hence the check for the returned scatter-gather must be using
the inline function IS_ERR_OR_NULL() in place of IS_ERR()
Signed-off-by: NSubash Patel <subash.ramaswamy@linaro.org>
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_dmabuf.c

@@ -214,7 +214,7 @@ struct drm_gem_object *exynos_dmabuf_prime_import(struct drm_device *drm_dev,
 
 
 	sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
-	if (IS_ERR(sgt)) {
+	if (IS_ERR_OR_NULL(sgt)) {
 		ret = PTR_ERR(sgt);
 		goto err_buf_detach;
 	}