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>