hwmon/w83627ehf: Preserve speed reading when changing fan min

The w83627ehf driver changes the fan clock divider automatically when
a new min fan speed is set. It is supposed to preserve the fan speed
reading while doing so, bug doesn't really. Fix it.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>

drivers/hwmon/w83627ehf.c

@@ -716,10 +716,15 @@ store_fan_min(struct device *dev, struct device_attribute *attr,
 	/* Write both the fan clock divider (if it changed) and the new
 	   fan min (unconditionally) */
 	if (new_div != data->fan_div[nr]) {
-		if (new_div > data->fan_div[nr])
-			data->fan[nr] >>= (data->fan_div[nr] - new_div);
-		else
-			data->fan[nr] <<= (new_div - data->fan_div[nr]);
+		/* Preserve the fan speed reading */
+		if (data->fan[nr] != 0xff) {
+			if (new_div > data->fan_div[nr])
+				data->fan[nr] >>= new_div - data->fan_div[nr];
+			else if (data->fan[nr] & 0x80)
+				data->fan[nr] = 0xff;
+			else
+				data->fan[nr] <<= data->fan_div[nr] - new_div;
+		}
 
 		dev_dbg(dev, "fan%u clock divider changed from %u to %u\n",
 			nr + 1, div_from_reg(data->fan_div[nr]),