iio: light: ltr501: Drop ACPI_PTR() usage

iio: light: ltr501: 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.

Include linux/mod_devicetable.h which includes the definition of
struct acpi_device_id (hence somewhat related to the main change)

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20231231183514.566609-15-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>