Fix invalid format string in HASH_DEBUG code
This seems to have been broken back in
be0a66666.
Reported-by: Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>
Author: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/OSCPR01MB14966E11EEFB37D7857FCEDB7F535A@OSCPR01MB14966.jpnprd01.prod.outlook.com
Backpatch-through: 14