mm/vmscan.c:shrink_folio_list(): save a tabstop

mm/vmscan.c:shrink_folio_list(): save a tabstop

We have some needlessly deep indentation in this huge function due to

	if (expr1) {
		if (expr2) {
			...
		}
	}

Convert this to

	if (expr1 && expr2) {
		...
	}

Also, reflow that big block comment to fit in 80 cols.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>