mm/mglru: improve struct lru_gen_mm_walk

mm/mglru: improve struct lru_gen_mm_walk

Rename max_seq to seq in struct lru_gen_mm_walk to keep consistent with
struct lru_gen_mm_state.  Note that seq is not always up to date with
max_seq from lru_gen_folio.

No functional changes.

Link: https://lkml.kernel.org/r/20240214060538.3524462-5-kinseyho@google.com
Signed-off-by: Kinsey Ho <kinseyho@google.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Donet Tom <donettom@linux.vnet.ibm.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>