hwmon: (sht15) Fix integer overflow in humidity calculation

commit ccd32e73 upstream.

An integer overflow occurs in the calculation of RHlinear when the
relative humidity is greater than around 30%. The consequence is a subtle
(but noticeable) error in the resulting humidity measurement.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/hwmon/sht15.c

@@ -333,11 +333,11 @@ static inline int sht15_calc_humid(struct sht15_data *data)
 
 	const int c1 = -4;
 	const int c2 = 40500; /* x 10 ^ -6 */
-	const int c3 = -2800; /* x10 ^ -9 */
+	const int c3 = -28; /* x 10 ^ -7 */
 
 	RHlinear = c1*1000
 		+ c2 * data->val_humid/1000
-		+ (data->val_humid * data->val_humid * c3)/1000000;
+		+ (data->val_humid * data->val_humid * c3) / 10000;
 	return (temp - 25000) * (10000 + 80 * data->val_humid)
 		/ 1000000 + RHlinear;
 }