iio: adc: cpcap-adc: remove redundant assignment to variable cal_data_diff

The variable cal_data_diff is being assigned a value that is never read,
it is being re-assigned later on with a new value in both paths of an
if statement. The assignment is redundant, so remove it.
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220207135943.340629-1-colin.i.king@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/cpcap-adc.c

@@ -474,7 +474,7 @@ static int cpcap_adc_calibrate_one(struct cpcap_adc *ddata,
 	for (i = 0; i < CPCAP_ADC_MAX_RETRIES; i++) {
 		calibration_data[0]  = 0;
 		calibration_data[1]  = 0;
-		cal_data_diff = 0;
+
 		cpcap_adc_setup_calibrate(ddata, channel);
 		error = regmap_read(ddata->reg, calibration_register,
 				    &calibration_data[0]);