I'm not sure how to wire up the LED Matrix corrctly. I followed the steps in this guide: https://github.com/hzeller/rpi-rgb-led-matrix/blob/master/wiring.md In this tutorial the matrix has 3 GND pins. But in the wiring diagram below the GND is only connected with 1 pin (pin no. 6). Can I also use the pins 9 and 14 for the other GND or must all GND wires connected with the same pin?