Btrfs: change BUG_ON()'s to ASSERT()'s in backref_cache_cleanup()

Since it is just an in-memory building of the backrefs of several
btree blocks, nothing is fatal other than memory leaks, so this
changes BUG_ON()'s to ASSERT()'s.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -235,12 +235,12 @@ static void backref_cache_cleanup(struct backref_cache *cache)
 	cache->last_trans = 0;
 
 	for (i = 0; i < BTRFS_MAX_LEVEL; i++)
-		BUG_ON(!list_empty(&cache->pending[i]));
-	BUG_ON(!list_empty(&cache->changed));
-	BUG_ON(!list_empty(&cache->detached));
-	BUG_ON(!RB_EMPTY_ROOT(&cache->rb_root));
-	BUG_ON(cache->nr_nodes);
-	BUG_ON(cache->nr_edges);
+		ASSERT(list_empty(&cache->pending[i]));
+	ASSERT(list_empty(&cache->changed));
+	ASSERT(list_empty(&cache->detached));
+	ASSERT(RB_EMPTY_ROOT(&cache->rb_root));
+	ASSERT(!cache->nr_nodes);
+	ASSERT(!cache->nr_edges);
 }
 
 static struct backref_node *alloc_backref_node(struct backref_cache *cache)