pinctrl: bcm281xx: Fix incorrect regmap max_registers value

pinctrl: bcm281xx: Fix incorrect regmap max_registers value

The max_registers value does not take into consideration the stride;
currently, it's set to the number of the last pin, but this does not
accurately represent the final register.

Fix this by multiplying the current value by 4.

Fixes: 54b1aa5a5b16 ("ARM: pinctrl: Add Broadcom Capri pinctrl driver")
Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
Link: https://lore.kernel.org/20250207-bcm21664-pinctrl-v1-2-e7cfac9b2d3b@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>