drm/radeon: r6xx/r7xx: fix possible oops in r600_page_table_cleanup()

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/r600_cp.c

@@ -121,6 +121,9 @@ void r600_page_table_cleanup(struct drm_device *dev, struct drm_ati_pcigart_info
 	int pages;
 	int i;
 
+	if (!entry)
+		return;
+
 	if (gart_info->bus_addr) {
 		max_pages = (gart_info->table_size / sizeof(u32));
 		pages = (entry->pages <= max_pages)