CVE-2026-72371: afs: Fix the volume AFS_VOLUME_RM_TREE is set on

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

afs: Fix the volume AFSVOLUMERMTREE is set on

Fix afsinsertvolumeintocell() to set AFSVOLUMERMTREE on the volume replaced, not the new volume, as it's now removed from the cell's volume tree. This will cause the old volume to be removed from the tree twice and the new volume never to be removed.