iio: potentiometer: max5487: Drop ACPI_PTR() usage

iio: potentiometer: max5487: Drop ACPI_PTR() usage

Avoiding unused variable warnings when using this macro adds
complexity that in simple cases like this one is not justified
for the small saving in data.

Switch include from acpi.h to mod_devicetable.h which includes the
definition of struct acpi_device_id.

Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20231231183514.566609-21-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>