md: fix problems with RAID6 calculations for DDF.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index dcefdc9..dd70835 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -488,7 +488,7 @@
 {
 	return (layout >= 0 && layout <= 5)
 		||
-		(layout == 8 || layout == 10)
+		(layout >= 8 && layout <= 10)
 		||
 		(layout >= 16 && layout <= 20);
 }