btrfs: pass NULL as trans to btrfs_search_slot if we only want to search

Using a transaction in btrfs_search_slot is only useful when we are
searching to add or modify the tree. When the function is used for
searching, insert length and mod arguments are 0, there is no need to
use a transaction.

No functional changes, changing for consistency.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -1211,7 +1211,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 again:
 	head = NULL;
 
-	ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
+	ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
 	if (ret < 0)
 		goto out;
 	BUG_ON(ret == 0);

fs/btrfs/extent-tree.c

@@ -153,7 +153,7 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 	else
 		key.type = BTRFS_EXTENT_ITEM_KEY;
 
-	ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
+	ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
 	if (ret < 0)
 		goto out_free;