software node: Also support referencing non-constant software nodes

Fwnode references are be implemented differently if referenced node is a
software node. _Generic() is used to differentiate between the two cases
but only const software nodes were present in the selection. Also add
non-const software nodes.

Reported-by: Kenneth Crudup <kenny@panix.com>
Closes: https://lore.kernel.org/all/af773b82-bef2-4209-baaf-526d4661b7fc@panix.com/
Fixes: d7cdbbc ("software node: allow referencing firmware nodes")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-By: Kenneth R. Crudup <kenny@panix.com>
Tested-by: Mehdi Djait <mehdi.djait@linux.intel.com> # Dell XPS 9315
Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Link: https://patch.msgid.link/20251219083638.2454138-1-sakari.ailus@linux.intel.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Sakari Ailus

include/linux/property.h

@@ -371,6 +371,7 @@ struct software_node_ref_args {
 (const struct software_node_ref_args) {				\
 	.swnode = _Generic(_ref_,				\
 			   const struct software_node *: _ref_,	\
+			   struct software_node *: _ref_,	\
 			   default: NULL),			\
 	.fwnode = _Generic(_ref_,				\
 			   struct fwnode_handle *: _ref_,	\