p9dsu: detect variant in init only if probe fails to found.
p9dsu: detect variant in init only if probe fails to found.

Currently the slot table init happens twice in both probe and init
functions due to the variant detection logic called with in-correct
condition check.

Fixes: d32ddea9 ("p9dsu: detect p9dsu variant even when hostboot
doesn't tell us")

Signed-off-by: Pridhiviraj Paidipeddi <fd8ea14509c256cbd04eaa4ee745a213945e70a1@linux.vnet.ibm.com>
[stewart: renanem variant-detected to p9dsu-riser-detected]
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

qemu/skiboot,qemu/skiboot,shenki/skiboot,qemu/skiboot,stewart-ibm/skiboot,open-power/skiboot,shenki/skiboot,stewart-ibm/skiboot,open-power/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot,legoater/skiboot,legoater/skiboot,open-power/skiboot,open-power/skiboot,shenki/skiboot,qemu/skiboot,legoater/skiboot,legoater/skiboot,stewart-ibm/skiboot,qemu/skiboot,legoater/skiboot