btrfs: restore BTRFS_SEQ_LAST when looking up qgroup backref lookup

In the patch a2c8d27 ("btrfs: use a structure to pass arguments to
backref walking functions") Filipe converted everybody to using a new
context struct to use for backref lookups, but accidentally dropped the
BTRFS_SEQ_LAST usage that exists for qgroups.  Add this back so we have
the previous behavior.

Fixes: a2c8d27 ("btrfs: use a structure to pass arguments to backref walking functions")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/qgroup.c

@@ -2787,6 +2787,7 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans)
 			 * current root. It's safe inside commit_transaction().
 			 */
 			ctx.trans = trans;
+			ctx.time_seq = BTRFS_SEQ_LAST;
 			ret = btrfs_find_all_roots(&ctx, false);
 			if (ret < 0)
 				goto cleanup;