CVE-2026-74426 afs: fix NULL pointer dereference in afs_get_tree()

In the Linux kernel, the following vulnerability has been resolved: afs: fix NULL pointer dereference in afsgettree afsallocsbi uses kzalloc for memory allocation. And, if ctx-dynroot is not null, as-cell and as-volume are null. In traceafsgettree they are dereferenced. KASAN error message: KASAN...