CVE-2026-63879

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

drm/amdgpu: fix amdgpu_hmm_range_get_pages

The notifier sequence must only be read once or otherwise we could work
with invalid pages.

While at it also fix the coding style, e.g. drop the pre-initialized
return value and use the common define for 2G range.

(cherry picked from commit c08972f555945cda57b0adb72272a37910153390)