md/md-bitmap: fix dm-raid max_write_behind setting

It's supposed to be COUNTER_MAX / 2, not COUNTER_MAX.

Link: https://lore.kernel.org/linux-raid/20250524061320.370630-14-yukuai1@huaweicloud.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Author: YuKuai-huawei

drivers/md/md-bitmap.c

@@ -789,7 +789,7 @@ static int md_bitmap_new_disk_sb(struct bitmap *bitmap)
 	 * is a good choice?  We choose COUNTER_MAX / 2 arbitrarily.
 	 */
 	write_behind = bitmap->mddev->bitmap_info.max_write_behind;
-	if (write_behind > COUNTER_MAX)
+	if (write_behind > COUNTER_MAX / 2)
 		write_behind = COUNTER_MAX / 2;
 	sb->write_behind = cpu_to_le32(write_behind);
 	bitmap->mddev->bitmap_info.max_write_behind = write_behind;