message: Fix incorrect path to rpi cross compiler
diff: set(CMAKE_SYSTEM_NAME "arm-linux-gnueabihf")
  # Location of pi toolchain
  -set(PI_TOOLCHAIN "/opt/rpi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/")
  +set(PI_TOOLCHAIN "/opt/rpi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf")
  # specify the cross compiler
  set(CMAKE_C_COMPILER "${PI_TOOLCHAIN}/bin/arm-linux-gnueabihf-gcc")
  