2 buttons, 1 servo, turn when pressed only
If you want the logic "if none of the two buttons are pressed, stop the servo immediately", then you'd express this in your loop as a if expression where you check if both buttons read LOW:

void loop()
{
  buttonStateCW = digitalRead(buttonPinCW);
  buttonStateCC = digitalRead(buttonPinCC);
  // clockwise rotation
  if (buttonStateCW == HIGH) {
    myservo.write(crSpeedCW);
    // counterclockwise rotation
  } 
  if (buttonStateCC == HIGH) {
    myservo.write(crSpeedCC);
  }

  //Are both buttons not pressed? 
  if(buttonStateCC == LOW &amp;&amp; buttonStateCW == LOW) {
    //Stop the servo.
    myservo.write(0);
  }
}


This assumes your buttons are with pull-down resistors to GND on one side and with +5V on the other side, as detailed in the Arduino tutorial. In short this means that an unpressed button reads as 0 and a pressed on reads as 1 (HIGH). This is unusual because we usually use the internal pullup resistors via the INPUT_PULLUP pinMode parameter with a switched logic (1 = unpressed, 0 = pressed).

I've also removed the line crServo = digitalRead(crSpeedDefault); because that doesn't make sense in my opinion, as I've detailed in my comment.