software node: Use software_node_unregister() when unregistering group of nodes

software node: Use software_node_unregister() when unregistering group of nodes

After the commit
  321718fbcc47 ("software node: implement software_node_unregister()")
has been applied a new helper appears that may be utilised in other places.
For time being there is one such place, i.e. in
software_node_unregister_node_group() which will benefit of the clean up.

Use software_node_unregister() when unregistering group of nodes.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200622082108.25577-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>