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

This function has been able to return LRU_STOP since commit b49547ade3
("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>

mm/zswap.c

@@ -1186,7 +1186,7 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
 
 	/*
 	 * It's safe to drop the lock here because we return either
-	 * LRU_REMOVED_RETRY or LRU_RETRY.
+	 * LRU_REMOVED_RETRY, LRU_RETRY or LRU_STOP.
 	 */
 	spin_unlock(&l->lock);