i2c: piix4: Fix port number check on release

The port number shift is still hard-coded to 1 while it now depends
on the hardware.

Thankfully 0 is always 0 no matter how you shift it, so this was a
bug without consequences.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Fixes: 0fe16195 ("i2c: piix4: Fix SMBus port selection for AMD Family 17h chips")
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>