fix warnings in sensor.cpp
fix warnings in sensor.cpp

IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense