Add calls to device_sync() for outputs when benchmarking
Add calls to device_sync() for outputs when benchmarking

kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide