I'm asking because I accidentally used my last Kelpsy Berry that I was going to use for planting.

There are 10 possible berries you can receive. You get 2 from the berry master. I don't know if they can be the same or not so I'll do 2 calculations.

Can be same berry: This easy. You have a 2/10 chance here so your chances are 1/5 or 20%

Can not be same berry: The fraction is a bit different. The first berry is 1/10 and the second is 1/9. So 9/90 + 10/90 = 19/90. That's approximately 21%.