PSI registers are 64-bit.

Spotted by Coverity: CID 1399704
Signed-off-by: NGreg Kurz <groug@kaod.org>
Message-Id: <155248884690.893204.5428179144527749023.stgit@bahia.lan>
Reviewed-by: NCédric Le Goater <clg@kaod.org>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>