Since you are not a party to the sale deed, you do not have to take any steps to cancel the sale deed.
Moreover since the partition suit is going on, once the court decides about your share with identification and separate possession of your share, then there is no question of cancelling the sale deed, the buyer has to obey the court order.
You can very well implead the buyer as part to the suit but if you have to file an application seeking to cancel the sale deed, you may have to file an amendment petition to amend the prayer as well as pleadings and you may have to pay the court fee also for this.
As the buyer bought this property intentionally very well knowing about the pending litigation on the property, he cannot harm you in this regard.