CVE-2026-98447: xfs: fix wild memcpy access when formatting ondisk rtrefcount btree roots

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

xfs: fix wild memcpy access when formatting ondisk rtrefcount btree roots

LOLLM noticed that the inode btree root formatting methods copy too many bytes -- there's only one set of keys in node blocks, not two. This causes memory corruption of whatever's beyond the buffers.