hw/imc: don't access homer memory if it was not initialised
hw/imc: don't access homer memory if it was not initialised

This can happen under mambo, at least.

Signed-off-by: Nicholas Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@gmail.com>
Reviewed-by: Madhavan Srinivasan <50c9fed97c2a760bbf32e7fdccf39ca6a997eabd@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

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