ATMEL SAMD11 SPI (Slave) With Arduino (Master)
You haven't set your SS pin as an output anywhere in your code.  

The arduino page you linked to has a note near the bottom which reads:  


  Note about Slave Select (SS) pin on AVR based boards
  
  All AVR based boards have an SS pin that is useful when they act as a
  slave controlled by an external master. Since this library supports
  only master mode, this pin should be set always as OUTPUT otherwise
  the SPI interface could be put automatically into slave mode by
  hardware, rendering the library inoperative. It is, however, possible
  to use any pin as the Slave Select (SS) for the devices. For example,
  the Arduino Ethernet shield uses pin 4 to control the SPI connection
  to the on-board SD card, and pin 10 to control the connection to the
  Ethernet controller.  


The Example code given for the teensy board on the other page you linked has:  

pinMode (slaveSelectPin, OUTPUT); 


in its setup() function.

So that's what you're missing.
Setting the pin high or low is not going to achieve anything if its not an output.  

Remember that SPI can access many diffrent devices using the same MOSI/MISO/SCK pins, but each slave device has its own Slave-Select pin which needs to be individually driven by the master.
Your master can therefore have many different SS pins, all set as outputs - and there is no single standard pin for this.