mfd: hi655x-pmic: Fixup issue with un-acked interrupts

While trying to get the powerkey to function, I found when
pressing the key, I would get infinitely repeating interrupts.

After digging around a bit, it seems we didn't set the ack_base
value for the regmap irqchip logic, so nothing was acking the
interrupt.

This patch adds the ack_base, which seems to make things work.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>