CVE-2026-98178: drm/amdgpu: Skip KFD mapping clear before initialization

In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu: Skip KFD mapping clear before initialization

amdgpuamdkfdclearkfdmapping() assumes that a non-NULL kfddev has a fully populated node array. This is not true when KFD device initialization fails after probe.

For example, kgd2kfddeviceinit() sets numnodes before checking PCIe atomics support. On Polaris systems without the required atomics, it returns before allocating nodes[0], but the kfddev remains attached to the amdgpu device. A later GPU reset then dereferences nodes[0]->id.

Require the authoritative KFD initialization flag before walking the node array, matching the existing KFD reset and teardown paths.

(cherry picked from commit 4ac1835823c47903fbb278bbf474773c46f59edc)