ACPI: property: Constify stubs for CONFIG_ACPI=n case

There is a few stubs that left untouched during constification of
the fwnode related APIs. Constify three more stubs here.

Fixes: 8b9d6802 ("ACPI: Constify acpi_bus helper functions, switch to macros")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>