iio: proximity: sx9500: Assign interrupt from GpioIo()

The commit 0f079650

("iio: remove gpio interrupt probing from drivers that use a single interrupt")

removed custom IRQ assignment for the drivers which are enumerated via
ACPI or OF. Unfortunately, some ACPI tables have IRQ line defined as
GpioIo() resource and thus automatic IRQ allocation will fail.

Partially revert the commit 0f079650

 to restore original behaviour.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>