samples: usb: hid: Enable harness for the sample

Enable harness so we can execute smoke tests on the hardware with
command line:
sanitycheck --device-testing --device-serial /dev/ttyACM0 -p <BOARD>
  -T samples/subsys/usb/hid

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>