bcache: Minor btree cache fix

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/btree.c

@@ -714,14 +714,10 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
 		}
 	}
 
-	/*
-	 * Can happen right when we first start up, before we've read in any
-	 * btree nodes
-	 */
-	if (list_empty(&c->btree_cache))
-		goto out;
-
 	for (i = 0; (nr--) && i < c->bucket_cache_used; i++) {
+		if (list_empty(&c->btree_cache))
+			goto out;
+
 		b = list_first_entry(&c->btree_cache, struct btree, list);
 		list_rotate_left(&c->btree_cache);