bcache: move calc_cached_dev_sectors to proper place on backing device detach

Calculation of cache_set's cached sectors is done by travelling
cached_devs list as shown below:

static void calc_cached_dev_sectors(struct cache_set *c)
{
...
        list_for_each_entry(dc, &c->cached_devs, list)
                sectors += bdev_sectors(dc->bdev);

        c->cached_dev_sectors = sectors;
}

But cached_dev won't be unlinked from c->cached_devs list until we call
following list_move(&dc->list, &uncached_devices),
so previous fix in 'commit 46010141da
("bcache: recal cached_dev_sectors on detach")' is wrong, now we move
it to its right place.

Signed-off-by: Lin Feng <linf@wangsu.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20211020143812.6403-5-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -1154,9 +1154,9 @@ static void cached_dev_detach_finish(struct work_struct *w)
 
 	mutex_lock(&bch_register_lock);
 
-	calc_cached_dev_sectors(dc->disk.c);
 	bcache_device_detach(&dc->disk);
 	list_move(&dc->list, &uncached_devices);
+	calc_cached_dev_sectors(dc->disk.c);
 
 	clear_bit(BCACHE_DEV_DETACHING, &dc->disk.flags);
 	clear_bit(BCACHE_DEV_UNLINK_DONE, &dc->disk.flags);