mfd: axp20x: Use IRQF_TRIGGER_LOW on the axp288

The interrupt line of the entire family of axp2xx pmics is active-low,
for devicetree enumerated irqs, this is dealt with in the devicetree.

ACPI irq resources have a flag field for this too, I tried using this
on my CUBE iwork8 Air tablet, but it does not contain the right data.

The dstd shows the irq listed as either ActiveLow or ActiveHigh,
depending on the OSID variable, which seems to be set by the
"OS IMAGE ID" in the BIOS/EFI setup screen.

Since the acpi-resource info is no good, simply pass in IRQF_TRIGGER_LOW
on the axp288.

Together with the other axp288 fixes in this series, this fixes the axp288
irq contineously triggering.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>