kernel: drm/amdgpu: prevent NULL pointer dereference if ATIF is not supported

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: prevent NULL pointer dereference if ATIF is not supported acpievaluateobject may return AENOTFOUND failure, which would result in dereferencing buffer.pointer obj while being NULL. Although this case may be unrealisti...