hwmon: (amc6821) sign extension temperature

commit 4538bfbf upstream.

Converts the unsigned temperature values from the i2c read
to be sign extended as defined in the datasheet so that
negative temperatures are properly read.

Fixes: 28e6274d ("hwmon: (amc6821) Avoid forward declaration")
Signed-off-by: Jared Bents <jared.bents@rockwellcollins.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
[groeck: Dropped unnecessary continuation line]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwmon/amc6821.c

@@ -188,8 +188,8 @@ static struct amc6821_data *amc6821_update_device(struct device *dev)
 			!data->valid) {
 
 		for (i = 0; i < TEMP_IDX_LEN; i++)
-			data->temp[i] = i2c_smbus_read_byte_data(client,
-				temp_reg[i]);
+			data->temp[i] = (int8_t)i2c_smbus_read_byte_data(
+				client, temp_reg[i]);
 
 		data->stat1 = i2c_smbus_read_byte_data(client,
 			AMC6821_REG_STAT1);