ACPI: property: Ignore already existing data node tags

ACPI node pointers are attached to data node handles, in order to resolve
string references to them. _DSD guide allows the same node to be reached
from multiple parent nodes, leading the node enumeration algorithm to each
such nodes more than once. As attached data already already exists,
attaching data with the same tag will fail. Address this problem by
ignoring nodes that have been already tagged.

Fixes: 1d52f109 ("ACPI: property: Tie data nodes to acpi handles")
Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>