iio:adc:qcom-spmi-vadc: use div64_s64 instead of direct 64 bit division.

Another one of these that we missed previously which prevents test builds
of this driver on 32 bit platforms as it gives an undefined __divdi3 warning.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/qcom-spmi-vadc.c

@@ -641,7 +641,7 @@ static int vadc_scale_therm(struct vadc_priv *vadc,
 	vadc_scale_calib(vadc, adc_code, prop, &voltage);
 
 	if (prop->calibration == VADC_CALIB_ABSOLUTE)
-		voltage /= 1000;
+		voltage = div64_s64(voltage, 1000);
 
 	vadc_map_voltage_temp(adcmap_100k_104ef_104fb,
 			      ARRAY_SIZE(adcmap_100k_104ef_104fb),