dm raid: remove WARN_ON() in raid10_md_layout_to_format()

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-raid.c

@@ -564,9 +564,10 @@ static const char *raid10_md_layout_to_format(int layout)
 	if (__raid10_near_copies(layout) > 1)
 		return "near";
 
-	WARN_ON(__raid10_far_copies(layout) < 2);
-
+	if (__raid10_far_copies(layout) > 1)
 		return "far";
+
+	return "unknown";
 }
 
 /* Return md raid10 algorithm for @name */