regulator: tps62360: Simplify tps62360_set_voltage_time_sel implementation

For linear mappings, we can use below equation to get the voltage difference
between new_selector and old_selector:

abs(new_selector - old_selector) * rdev->desc->uV_step
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/tps62360-regulator.c

@@ -179,17 +179,10 @@ static int tps62360_set_voltage_time_sel(struct regulator_dev *rdev,
 		unsigned int old_selector, unsigned int new_selector)
 {
 	struct tps62360_chip *tps = rdev_get_drvdata(rdev);
-	int old_uV, new_uV;
 
-	old_uV = regulator_list_voltage_linear(rdev, old_selector);
-	if (old_uV < 0)
-		return old_uV;
-
-	new_uV = regulator_list_voltage_linear(rdev, new_selector);
-	if (new_uV < 0)
-		return new_uV;
-
-	return DIV_ROUND_UP(abs(old_uV - new_uV), tps->change_uv_per_us);
+	return DIV_ROUND_UP(abs(new_selector - old_selector) *
+			    rdev->desc->uV_step,
+			    tps->change_uv_per_us);
 }
 
 static int tps62360_set_mode(struct regulator_dev *rdev, unsigned int mode)