i2c: piix4: remove unneeded assignments

smatch rightfully says:
drivers/i2c/busses/i2c-piix4.c:504 piix4_access warn: unused return: i = inb_p()
drivers/i2c/busses/i2c-piix4.c:537 piix4_access warn: unused return: i = inb_p()

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Tested-by: Christian Fetzer <fetzer.ch@gmail.com>