Updated Mac drivers for FTDI serial on BeagleBone

FTDI did update their drivers and I found that the FTDI drivers I was providing didn’t install properly on Mountain Lion. I’ve updated the drivers on the github.

https://github.com/beagleboard/beaglebone-getting-started/commit/6f690234e32038477bda6a04c62fe30aa415a54a

This most impacts BeagleBones earlier than rev A5, because they would otherwise need to patch the FTDI driver install files themselves. Other users can simply download the drivers from FTDI.