power: supply: ab8500_fg: Request all IRQs as threaded

Since these IRQs are cascaded from a nested IRQ, the
generic IRQ system detects this and refuse to deliver
a fastpath IRQ in response to request_irq():

  nested = irq_settings_is_nested_thread(desc);
  if (nested) {
          if (!new->thread_fn) {
                  ret = -EINVAL;
                  goto out_mput;
          }
   (...)

Threaded IRQs work just as well so let's just request
threaded IRQs. One of the IRQs are alread requested
as threaded anyways.

Cc: Marcus Cooper <codekipper@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>