It's possible to be a living liver donor after having donated a kidney. The incidence of doing so is very rare. I'm aware of only a couple of people who have done this.
One barrier is that transplant centers aren't keen on subjecting someone who has already given a kidney to another surgery, and one that diminishes additional organ function. (While the liver "regenerates," it doesn't assume it's original anatomy or full function.) Another barrier is the absence of medical research that indicates the long-term impact of giving up both a kidney and portion of your liver. No one really knows what that means for the health of the donor.
So, yes, it's possible, but it is uncommon.