doc: cosmetic fixup of reference to stale header
doc: cosmetic fixup of reference to stale header

Signed-off-by: Balbir singh <ac7b77b73f9d2cc0faddd296218dde0558e170e3@gmail.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

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