Swap SPI mode 3 to mode 0

Fixes an incompatibilty with the Ethernet library depending on which
order you initialise in. The SSD1351 datasheet suggests clock should
idle high, but experience suggests it doesn't matter.

As per http://forum.freetronics.com/viewtopic.php?f=37&t=5543&sid=794f42bd9369da5bec2d6affbc360ea1