ppc440_uc: Fix a copy/paste error

Missed in 3c409c19, hopefully reported by Coverity.

Fixes: Coverity CID 1393788 (Copy-paste error)
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>