samples: fxos8700: Decimate sensor data before printing to the console

At the default sample rate of 400 Hz, there is not enough bandwidth on
the UART at 115200 baud to print every sample. Fix by decimating the
sensor data by 4 before printing to the console.

This issue was discovered after fixing ZEP-1507.

Change-Id: I451ec9873ca93fe417d5d5a2d6d13b5e921c7611
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>