hwmon: (k10temp) Only apply temperature offset if result is positive

A user reports a really bad temperature on Ryzen 1950X.

k10temp-pci-00cb
Adapter: PCI adapter
temp1: +4294948.3°C (high = +70.0°C)

This will happen if the temperature reported by the chip is lower than
the offset temperature. This has been seen in the field if "Sense MI Skew"
and/or "Sense MI Offset" BIOS parameters were set to unexpected values.
Let's report a temperature of 0 degrees C in that case.

Fixes: 1b50b77 ("hwmon: (k10temp) Add support for temperature offsets")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: groeck

drivers/hwmon/k10temp.c

@@ -129,7 +129,10 @@ static ssize_t temp1_input_show(struct device *dev,
 
 	data->read_tempreg(data->pdev, &regval);
 	temp = (regval >> 21) * 125;
-	temp -= data->temp_offset;
+	if (temp > data->temp_offset)
+		temp -= data->temp_offset;
+	else
+		temp = 0;
 
 	return sprintf(buf, "%u\n", temp);
 }