memcg: workingset: remove folio_memcg_rcu usage

The function workingset_activation() is called from folio_mark_accessed()
with the guarantee that the given folio can not be freed under us in
workingset_activation().  In addition, the association of the folio and
its memcg can not be broken here because charge migration is no more. 
There is no need to use folio_memcg_rcu.  Simply use folio_memcg_charged()
because that is what this function cares about.

[akpm@linux-foundation.org: provide folio_memcg_charged stub for CONFIG_MEMCG=n]
Link: https://lkml.kernel.org/r/20241026163707.2479526-1-shakeel.butt@linux.dev


Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Suggested-by: Yu Zhao <yuzhao@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>