Update PWM.h
Update PWM.h

Fixed problem with polarity -- thanks Frank
chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone,chaicko/ExploringBeagleBone