maple_tree: fix mt_destroy_walk() on root leaf node

On destroy, we should set each node dead.  But current code miss this when
the maple tree has only the root node.

The reason is mt_destroy_walk() leverage mte_destroy_descend() to set node
dead, but this is skipped since the only root node is a leaf.

Fixes this by setting the node dead if it is a leaf.

Link: https://lore.kernel.org/all/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 54a611b ("Maple Tree: add new data structure")
Signed-off-by: Wei Yang <[email protected]>
Signed-off-by: Liam R. Howlett <[email protected]>
Reviewed-by: Dev Jain <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: RichardWeiYang

lib/maple_tree.c

@@ -5319,6 +5319,7 @@ static void mt_destroy_walk(struct maple_enode *enode, struct maple_tree *mt,
 	struct maple_enode *start;
 
 	if (mte_is_leaf(enode)) {
+		mte_set_node_dead(enode);
 		node->type = mte_node_type(enode);
 		goto free_leaf;
 	}