drm: simplify drm_sysfs_destroy() via IS_ERR_OR_NULL()

Simplify `foo == NULL || IS_ERR(foo)` via IS_ERR_OR_NULL(). This is
pretty commonly used all over the kernel, especially for debugfs/sysfs
cleanup paths.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_sysfs.c

@@ -156,7 +156,7 @@ err_out:
  */
 void drm_sysfs_destroy(void)
 {
-	if ((drm_class == NULL) || (IS_ERR(drm_class)))
+	if (IS_ERR_OR_NULL(drm_class))
 		return;
 	class_remove_file(drm_class, &class_attr_version.attr);
 	class_destroy(drm_class);