hwmon: (it87) Properly handle wrong sensor type requests

Currently, if someone tries to set the thermal sensor type to an
unsupported value, subsequent accesses to the chip may temporarily
show the sensor in question as disabled. Use a temporary variable
and only update the cached value on success, to prevent such
confusion.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/hwmon/it87.c

diff --git a/drivers/hwmon/it87.c b/drivers/hwmon/it87.c
index 5e39e2d..a65ba31 100644
--- a/drivers/hwmon/it87.c
+++ b/drivers/hwmon/it87.c
@@ -539,15 +539,14 @@
 
 	struct it87_data *data = dev_get_drvdata(dev);
 	long val;
+	u8 reg;
 
 	if (strict_strtol(buf, 10, &val) < 0)
 		return -EINVAL;
 
-	mutex_lock(&data->update_lock);
-
-	data->sensor = it87_read_value(data, IT87_REG_TEMP_ENABLE);
-	data->sensor &= ~(1 << nr);
-	data->sensor &= ~(8 << nr);
+	reg = it87_read_value(data, IT87_REG_TEMP_ENABLE);
+	reg &= ~(1 << nr);
+	reg &= ~(8 << nr);
 	if (val == 2) {	/* backwards compatibility */
 		dev_warn(dev, "Sensor type 2 is deprecated, please use 4 "
 			 "instead\n");
@@ -555,13 +554,14 @@
 	}
 	/* 3 = thermal diode; 4 = thermistor; 0 = disabled */
 	if (val == 3)
-		data->sensor |= 1 << nr;
+		reg |= 1 << nr;
 	else if (val == 4)
-		data->sensor |= 8 << nr;
-	else if (val != 0) {
-		mutex_unlock(&data->update_lock);
+		reg |= 8 << nr;
+	else if (val != 0)
 		return -EINVAL;
-	}
+
+	mutex_lock(&data->update_lock);
+	data->sensor = reg;
 	it87_write_value(data, IT87_REG_TEMP_ENABLE, data->sensor);
 	mutex_unlock(&data->update_lock);
 	return count;