xdu: Consistently indent with spaces

Fixes: commit efa72d7 (xdu: Initialize variables `name` in all cases)

xdu.c

@@ -885,7 +885,7 @@ void savepsnode(FILE * fp, struct node *nodep, struct rect rect, int showsize)
         name = label;
         break;
     default:
-	name = NULL;
+        name = NULL;
         break;
     }