i2c: piix4: Always use the same type for port

Sometimes u8 is used to store the port number, sometimes unsigned
short is used. Consistently stick to a single type, for consistency
and to avoid implicit casts.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>