ACPI: property: Make acpi_node_prop_read() static

There is no users outside of property.c. No need to export
acpi_node_prop_read(), hence make it static.

Fixes: 3708184a ("device property: Move FW type specific functionality to FW specific files")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>