prd: Fix FSP - HBRT firmware_notify message
prd: Fix FSP - HBRT firmware_notify message

Commit eb86b148 added FSP -> HBRT notify message support. I assumed that
we just need to construct `firmware notify` PRD message and pass it to
HBRT. But HBRT expects OPAL to pass `struct prd_fw_msg` message with
message type PRD_FW_MSG_TYPE_HBRT_FSP.

Fixes: eb86b148 (prd: Implement generic FSP - HBRT interface)
Cc: Daniel M. Crowell <912029ca9254ac7b5854e56910561d682e1fa2d0@us.ibm.com>
Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>
Signed-off-by: Oliver O'Halloran <3dfaff8fa6ae977f042064a112a6aac576279b9b@gmail.com>

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