drivers: base: swnode: Make two functions static

Fix sparse warning:

drivers/base/swnode.c:475:22: warning: symbol 'software_node_get_parent' was not declared. Should it be static?
drivers/base/swnode.c:484:22: warning: symbol 'software_node_get_next_child' was not declared. Should it be static?

Signed-off-by: YueHaibing <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/base/swnode.c

···
 						val, nval);
 }
 
-struct fwnode_handle *
+static struct fwnode_handle *
 software_node_get_parent(const struct fwnode_handle *fwnode)
 {
 	struct software_node *swnode = to_software_node(fwnode);
···
 			NULL;
 }
 
-struct fwnode_handle *
+static struct fwnode_handle *
 software_node_get_next_child(const struct fwnode_handle *fwnode,
 			     struct fwnode_handle *child)
 {