mm: ksm: drop KSM_KMEM_CACHE()

After commit 21fbd591 ("ksm: add the ksm prefix to the names of the
ksm private structures"), we could directly use KMEM_CACHE().

Link: https://lkml.kernel.org/r/20240618081201.134985-1-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>