God's omnipotence means that you can start any sentence with "God can..." and finish it arbitrarily, and it will be true. But you contradict when you say "God can end his omnipotence" for if God did this, He would no longer be able to do anything. God therefore cannot do this. Therefore, God is logically not omnipotent.
However, the fallacy in this argument is that it is a construction of language that may not signify anything in reality. Just because we can grammatically construct the above sentence does not mean that the sentence signifies something real. The separate pieces may signify things, such as the word "God" signifying the real God, and the word "can" signifying real potential and the word "omnipotence" signifying real omnipotence, but that does not mean that something real exists consisting of all those pieces put together.