SPI prescaling wrong? #22

Hi,

just in case someone is still working on this (would be great!)
I just read the code to understand why SPI does not work for me and found this:

It seems the prescale parameter is set by calculating it from clock freq / bus freq, then directly use that to call the framework init function.
But the framework init function seems to expect some 3-bit pattern which only allows distinct prescales of multiples of 2.
So, the SPI configuration is destroyed by this