God's omnipotence, as I understand it, entails that everything that has happened, is happening, or will happen, is caused by Him. This necessitates that it is impossible for anything to occur, past, present, or future, that was not ultimately caused by Him.
This is equivalent to saying that God can do anything that can be done, a more classical way of framing omnipotence, because, if it has not happened, and it is not happening, and it will not happen, then in what sense "can" it happen? It cannot. The only things that "can" happen are those things that have happened, are happening, or will happen, all of which are caused by God. Nothing else can happen.
Thus, God can do anything that can be done, the classical way of framing omnipotence.
God has never lied, is not lying, and will never lie. Thus, God lying cannot happen. Therefore, this is no infringement upon His omnipotence.
P2. Lying is something that can be done.
C1. God can lie (from P1 and P2)