Fix for support the raspberrypi kernel change on spi-max-frequency

[DanielChesters]

See raspberrypi/linux#2165 and piface/pifacecad/issues/24

[tompreston]

This was already merged I think https://github.com/piface/pifacecommon/pull/23

Edit: ah yes, I merged the other one as it also contained a version bump