bcachefs: Fix infinite loop in bch2_btree_cache_scan()

When attempting to free btree nodes, we might not be able to free all
the nodes that were requested. But the code was looping until it had
freed _all_ the nodes requested, when it should have only been
attempting to free nr nodes.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_cache.c

@@ -309,7 +309,7 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
 
 		touched++;
 
-		if (freed >= nr)
+		if (touched >= nr)
 			break;
 
 		if (!btree_node_reclaim(c, b)) {
@@ -323,7 +323,7 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
 	list_for_each_entry_safe(b, t, &bc->live, list) {
 		touched++;
 
-		if (freed >= nr) {
+		if (touched >= nr) {
 			/* Save position */
 			if (&t->list != &bc->live)
 				list_move_tail(&bc->live, &t->list);