samples: adxl372: switch i2c interface on frdm_k64f

Switch to using I2C0 as this I2C controller on the FRDM-K64F is actually
configured (pinmux) for use and is available on an arduino header if
someone would wire up an adxl372 to it.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>