gpio: pci-idio-16: Fix port memory offset for get_multiple callback

The ioread8 function expects a memory offset argument. This patch fixes
the ports array to provide the memory addresses of the respective device
I/O registers.

Fixes: 810ebfc5 ("gpio: pci-idio-16: Implement get_multiple callback")
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>