superio/f71869ad: fix documentation of io_info mask values

Change-Id: I5d0a945de45f8f4a77193135e63f480af14a0136
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: http://review.coreboot.org/6279
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>