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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/light/ltr501.c

···
  */
 
 #include <linux/module.h>
+#include <linux/mod_devicetable.h>
 #include <linux/i2c.h>
 #include <linux/err.h>
 #include <linux/delay.h>
···
 		.name   = LTR501_DRV_NAME,
 		.of_match_table = ltr501_of_match,
 		.pm	= pm_sleep_ptr(&ltr501_pm_ops),
-		.acpi_match_table = ACPI_PTR(ltr_acpi_match),
+		.acpi_match_table = ltr_acpi_match,
 	},
 	.probe = ltr501_probe,
 	.remove	= ltr501_remove,