Fix the "Initialization" in the Sysman Programming Guide

[bgoglin]

From https://spec.oneapi.io/level-zero/latest/sysman/PROG.html
"For compatibility, an application may also use the Level0 Core API to enumerate through available accelerator devices in the system. For each device handle, an application can cast it to a sysman device handle to manage the system resources of the device."
This cast is invalid when using ZesInit() as discussed in intel/compute-runtime#686, it's only valid when using zeInit() + the env var to enable Sysman. I asked for the fix there last year but the issue was closed without the spec fix.