A com_acpi_softc pointer is used as the interrupt callback cookie which

A com_acpi_softc pointer is used as the interrupt callback cookie which
is later on interpreted as a com_softc pointer. This is not a problem in
practice as a com_softc structure is the first member of the
com_acpi_softc structure.

Using the actual types consistently yields a better symmetry in my
opinion between registering the interrupt and the corresponding
interrupt handler.

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