powerpc/85xx: Wrong variable returned on error

The wrong variable was returned in the case of an error.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>