Wunused-variable: Fixed all unused variables in src

This commit addresses all warnings emitted from -Wunused-variable
in the C++ src.

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

src/max44009/max44009.cxx

@@ -64,7 +64,6 @@ MAX44009::reset() {
 
 uint16_t
 MAX44009::getVisibleRaw() {
-    uint8_t exponent, mantissa;
     uint8_t data[MAX44009_LUX_LENGTH];
     uint16_t* value = reinterpret_cast<uint16_t*>(&data[0]);