I was also getting the same error. But now it is working for me. First you install I2S microphone as shown here: https://learn.adafruit.com/adafruit-i2s-mems-microphone-breakout/raspberry-pi-wiring-and-test
After that while you are installing I2S amplifier go to the detailed installation section: https://learn.adafruit.com/adafruit-max98357-i2s-class-d-mono-amp/raspberry-pi-usage#detailed-install-5-16
and skip the first 2 stps and start from "Create asound.conf file" and at last reboot your pi.