iio: pressure: dps310: simplify scale factor reading

Both functions `dps310_get_pres_precision` and
`dps310_get_temp_precision` provide the oversampling rate by calling the
`BIT()` macro. However, to look up the corresponding scale factor, we
need the register value itself. Currently, this is achieved by undoing
the calculation of the oversampling rate with `ilog2()`.

Simplify the two functions for getting the scale factor and directly
use the register content for the lookup.
Signed-off-by: Thomas Haemmerle <thomas.haemmerle@leica-geosystems.com>
Link: https://lore.kernel.org/r/20240415105030.1161770-5-thomas.haemmerle@leica-geosystems.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/pressure/dps310.c

@@ -382,11 +382,11 @@ static int dps310_get_pres_k(struct dps310_data *data, int *val)
 {
 	int reg_val, rc;
 
-	rc = dps310_get_pres_precision(data, &reg_val);
-	if (rc)
+	rc = regmap_read(data->regmap, DPS310_PRS_CFG, &reg_val);
+	if (rc < 0)
 		return rc;
 
-	*val = scale_factors[ilog2(reg_val)];
+	*val = scale_factors[reg_val & GENMASK(2, 0)];
 
 	return 0;
 }
@@ -395,11 +395,11 @@ static int dps310_get_temp_k(struct dps310_data *data, int *val)
 {
 	int reg_val, rc;
 
-	rc = dps310_get_temp_precision(data, &reg_val);
-	if (rc)
+	rc = regmap_read(data->regmap, DPS310_TMP_CFG, &reg_val);
+	if (rc < 0)
 		return rc;
 
-	*val = scale_factors[ilog2(reg_val)];
+	*val = scale_factors[reg_val & GENMASK(2, 0)];
 
 	return 0;
 }