software node: Fix node registration

Software node can not be registered before its parent.

Fixes: 80488a6b ("software node: Add support for static node descriptors")
Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>