pinctrl/abx500: align GPIO cluster boundaries

Not quite sure how this ever worked. In ab8500_gpio_to_irq() the
GPIO for conversion is passed through as the second argument. If
GPIO13, which is a valid GPIO for IRQ functionality, was received;
it would be rejected by the following guard:

    GPIO_IRQ_CLUSTER(5, 12, 0); /* GPIO numbers start from 1 */

    if (offset >= cluster->start && offset <= cluster->end)
        /* Valid GPIO for IRQ use */

Signed-off-by: Lee Jones <lee.jones@linaro.org>
[Augmented to account for off-by-one problem]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>