llvm: Fixed remaining warnings for llvm

This commit addresses warnings emitted from the llvm
compilers which were not encountered with gnu.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/bmx055/bmm150.hpp

@@ -594,8 +594,6 @@ namespace upm {
 
   private:
     bool m_isSPI;
-    // use the FIFO by default?
-    bool m_useFIFO;
 
     // return a reference to a gpio pin pointer depending on intr
     mraa::Gpio*& getPin(INTERRUPT_PINS_T intr);