scripts/gdb: slab: update field names of struct kmem_cache

scripts/gdb: slab: update field names of struct kmem_cache

The commit 5ba6bc27b1f9 ("slab: decouple pointer to barn from
kmem_cache_node") reorganized the struct kmem_cache to factor out the
per-node fields to the new struct kmem_cache_per_node_ptrs.  This causes
the gdb scripts for lx-slabinfo and lx-slabtrace fail as they still
reference the old structure.

Adjust the gdb scripts to match the current state of struct kmem_cache.

Link: https://lore.kernel.org/20260427142448.666117-3-illia@yshyn.com
Fixes: 5ba6bc27b1f9 ("slab: decouple pointer to barn from kmem_cache_node")
Signed-off-by: Illia Ostapyshyn <illia@yshyn.com>
Acked-by: Harry Yoo (Oracle) <harry@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Florian Fainelli <florian.fainelli@broadcom.com>
Cc: Hao Li <hao.li@linux.dev>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Seongjun Hong <hsj0512@snu.ac.kr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>