Fix NULL pointer dereference
Fix NULL pointer dereference

Fix NULL pointer dereference in paca.c

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

V2: Use CHECK_SPPTR instead of NULL
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

shenki/skiboot,apopple/skiboot,shenki/skiboot,open-power/skiboot,apopple/skiboot,qemu/skiboot,ddstreet/skiboot,qemu/skiboot,qemu/skiboot,qemu/skiboot,stewart-ibm/skiboot,shenki/skiboot,open-power/skiboot,csmart/skiboot,shenki/skiboot,qemu/skiboot,open-power/skiboot,apopple/skiboot,mikey/skiboot,mikey/skiboot,open-power/skiboot,legoater/skiboot,ddstreet/skiboot,stewart-ibm/skiboot,legoater/skiboot,stewart-ibm/skiboot,csmart/skiboot,legoater/skiboot,open-power/skiboot,mikey/skiboot,csmart/skiboot,legoater/skiboot,ddstreet/skiboot,shenki/skiboot,legoater/skiboot