power: supply: max17040: Do not enforce (incorrect) interrupt trigger type

Interrupt line can be configured on different hardware in different way,
even inverted.  Therefore driver should not enforce specific trigger
type - edge falling - but instead rely on Devicetree to configure it.

The Maxim 14577/77836 datasheets describe the interrupt line as active
low with a requirement of acknowledge from the CPU therefore the edge
falling is not correct.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Iskren Chernev <iskren.chernev@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>