schema tree REFACTOR compatibility of lysp_module and lysp_submodule

Also, the main module can now be accessed directly.
diff --git a/src/tree_schema_helpers.c b/src/tree_schema_helpers.c
index 1fe1614..ad28cab 100644
--- a/src/tree_schema_helpers.c
+++ b/src/tree_schema_helpers.c
@@ -708,9 +708,9 @@
         assert(info->submoduleof);
 
         /* check that the submodule belongs-to our module */
-        if (strcmp(info->submoduleof, submod->belongsto)) {
+        if (strcmp(info->submoduleof, submod->mod->name)) {
             LOGVAL(ctx, LY_VLOG_NONE, NULL, LYVE_REFERENCE, "Included \"%s\" submodule from \"%s\" belongs-to a different module \"%s\".",
-                   submod->name, info->submoduleof, submod->belongsto);
+                   submod->name, info->submoduleof, submod->mod->name);
             return LY_EVALID;
         }
         /* check circular dependency */