[POWERPC] ps3: Fix no storage devices found

Fix probing of PS3 storage devices: in the success case, we should set
`error' to zero, not `result'.

Without this patch no storage devices are found.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>