gpio: pci-idio-16: Define maximum valid register address offset

Attempting to load the pci-idio-16 module fails during regmap
initialization with a return error -EINVAL. This is a result of the
regmap cache failing initialization. Set the idio_16_regmap_config
max_register member to fix this failure.

Fixes: 73d8f3ef ("gpio: pci-idio-16: Migrate to the regmap API")
Reported-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Closes: https://lore.kernel.org/r/9b0375fd-235f-4ee1-a7fa-daca296ef6bf@nutanix.com


Suggested-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Cc: stable@vger.kernel.org
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: William Breathitt Gray <wbg@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20251020-fix-gpio-idio-16-regmap-v2-2-ebeb50e93c33@kernel.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>