hdata: Replace hardcoded string with macro
hdata: Replace hardcoded string with macro

Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>
Reviewed-by: Dan Horák <2591e5f46f28d303f9dc027d475a5c60d8dea17a@danny.cz>
Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>

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