software node: Get reference to parent swnode in get_parent op

software node: Get reference to parent swnode in get_parent op

The software_node_get_parent() returned a pointer to the parent swnode,
but did not take a reference to it, leading the caller to put a reference
that was not taken. Take that reference now.

Fixes: 59abd83672f7 ("drivers: base: Introducing software nodes to the firmware node framework")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>