fix wrong operator use in stdlib/rand.c
fix wrong operator use in stdlib/rand.c

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

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