NFSv4.2: Fix missing removal of SLAB_ACCOUNT on kmem_cache allocation

The commit 5c60e89 ("NFSv4.2: Fix up an invalid combination of memory
allocation flags") has stripped GFP_KERNEL_ACCOUNT down to GFP_KERNEL,
however, it forgot to remove SLAB_ACCOUNT from kmem_cache allocation.
It means that memory is still limited by kmemcg.  This patch also fix a
NULL pointer reference issue [1] reported by NeilBrown.

Link: https://lore.kernel.org/all/164870069595.25542.17292003658915487357@noble.neil.brown.name/ [1]
Fixes: 5c60e89 ("NFSv4.2: Fix up an invalid combination of memory allocation flags")
Fixes: 5abc1e3 ("mm: list_lru: allocate list_lru_one only when needed")
Reported-by: NeilBrown <neilb@suse.de>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs42xattr.c

@@ -997,7 +997,7 @@ int __init nfs4_xattr_cache_init(void)
 
 	nfs4_xattr_cache_cachep = kmem_cache_create("nfs4_xattr_cache_cache",
 	    sizeof(struct nfs4_xattr_cache), 0,
-	    (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|SLAB_ACCOUNT),
+	    (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD),
 	    nfs4_xattr_cache_init_once);
 	if (nfs4_xattr_cache_cachep == NULL)
 		return -ENOMEM;