ir3: fix physical edges of predicated branches

The algorithm for adding extra physical edges works by finding edges that jump over reconvergence points. Since predicated branches don't introduce reconvergence points, we wouldn't add a physical edge from the true block to the false block. However, this physical edge is still needed as control flow does fall though here. This patch fixes this by manually adding the physical edge so that we don't need to insert a reconvergence point for it.