fix return value in backlight helper exe on non-freebsd systems
fix return value in backlight helper exe on non-freebsd systems

ref D2337

tasn/enlightenment,rvandegrift/e,rvandegrift/e,FlorentRevest/Enlightenment,tasn/enlightenment,tizenorg/platform.upstream.enlightenment,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment,tasn/enlightenment,rvandegrift/e,tizenorg/platform.upstream.enlightenment,FlorentRevest/Enlightenment