iio: accel: mma7660: Mark acpi match table as maybe unused

When building kernels without ACPI support the table is declared
but is not used because ACPI_PTR() turns it into a NULL.

Add the __maybe_unused attribute to stop the compiler whining.
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Link: https://lore.kernel.org/r/20210919072616.3849723-1-daniel@0x0f.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/mma7660.c

@@ -254,7 +254,7 @@ static const struct of_device_id mma7660_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, mma7660_of_match);
 
-static const struct acpi_device_id mma7660_acpi_id[] = {
+static const struct acpi_device_id __maybe_unused mma7660_acpi_id[] = {
 	{"MMA7660", 0},
 	{}
 };