gpio: 104-idio-16: Define maximum valid register address offset

Attempting to load the 104-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: 2c210c9 ("gpio: 104-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-v2-1-ebeb50e93c33@kernel.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: William Breathitt Gray

drivers/gpio/gpio-104-idio-16.c

@@ -59,6 +59,7 @@ static const struct regmap_config idio_16_regmap_config = {
 	.reg_stride = 1,
 	.val_bits = 8,
 	.io_port = true,
+	.max_register = 0x5,
 	.wr_table = &idio_16_wr_table,
 	.rd_table = &idio_16_rd_table,
 	.volatile_table = &idio_16_rd_table,