samples: bmi160: use correct spi dev name

The dev name for spi in the sensor sub-system was changed to
SPI_SS_x from SPI_x recently. Let's use the new name in the
sample app.

Change-Id: I78cdf21fce16290503c303e0de1432b4587486aa
Signed-off-by: Baohong Liu <baohong.liu@intel.com>
1 file changed