regulator: core: Fix error return for /sys access

regulator_uV_show() is missing error handling if regulator_get_voltage_rdev()
returns negative values. Instead it prints the errno as a string, e.g. -EINVAL
as "-22" which could be interpreted as -22 µV.

We also do not need to hold the lock while converting the integer to a string.

Reported-by: Adam Ford <[e-mail]>
Signed-off-by: H. Nikolaus Schaller <[e-mail]>
Tested-by: Adam Ford <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/core.c

···
 				struct device_attribute *attr, char *buf)
 {
 	struct regulator_dev *rdev = dev_get_drvdata(dev);
-	ssize_t ret;
+	int uV;
 
 	regulator_lock(rdev);
-	ret = sprintf(buf, "%d\n", regulator_get_voltage_rdev(rdev));
+	uV = regulator_get_voltage_rdev(rdev);
 	regulator_unlock(rdev);
 
-	return ret;
+	if (uV < 0)
+		return uV;
+	return sprintf(buf, "%d\n", uV);
 }
 static DEVICE_ATTR(microvolts, 0444, regulator_uV_show, NULL);