CVE-2026-63879 drm/amdgpu: fix amdgpu_hmm_range_get_pages

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: fix amdgpuhmmrangegetpages 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 comm...