mm/zswap: add LRU_STOP to comment about dropping the lru lock

mm/zswap: add LRU_STOP to comment about dropping the lru lock

This function has been able to return LRU_STOP since commit b49547ade38a
("mm/zswap: stop lru list shrinking when encounter warm region").  To
reduce confusion, update the comment to also list LRU_STOP as an option.

Link: https://lkml.kernel.org/r/20241127-lru-stop-comment-v1-1-f54a7cba9429@google.com
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>