hwmon: (stts751) buffer overrun on wrong chip configuration

If stts751 hw by some reason reports conversion rate bigger then 9:
ret = i2c_smbus_read_byte_data(priv->client, STTS751_REG_RATE);
then dereferencing stts751_intervals[priv->interval] leads to buffer
overrun.

The patch adds sanity check for value stored on chip.

Found by Linux Driver Verification project (linuxtesting.org).

Fixes: 7f07ec0fa17a ("hwmon: new driver for ST stts751 thermal sensor")
Signed-off-by: Anton Vasilyev <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/stts751.c

···
 	ret = i2c_smbus_read_byte_data(priv->client, STTS751_REG_RATE);
 	if (ret < 0)
 		return ret;
+	if (ret >= ARRAY_SIZE(stts751_intervals)) {
+		dev_err(priv->dev, "Unrecognized conversion rate 0x%x\n", ret);
+		return -ENODEV;
+	}
 	priv->interval = ret;
 
 	ret = stts751_read_reg16(priv, &priv->event_max,