Yep, normally any GND point should work. The best option would be to use a point directly connected to AGND, as this is the real reference for the feedback line, but as AGND and GND shouldn't differ by much (AGND should be less prone to interference), it should theoretically not matter at all if you used just GND instead. The difference between GND and AGND as reference should max. be in the mV range.