validation CHANGE validating single module data

... instead of module array. It simplifies the API
considerably and in case several modules need to
be validated, the function can be called repeatedly
without any performance impact.
diff --git a/src/parser_xml.c b/src/parser_xml.c
index c435643..8c1e36d 100644
--- a/src/parser_xml.c
+++ b/src/parser_xml.c
@@ -701,7 +701,7 @@
             if (validate_options & LYD_VALIDATE_PRESENT) {
                 mod = lyd_data_next_module(&next, &first);
             } else {
-                mod = lyd_mod_next_module(next, NULL, 0, ctx, &i, &first);
+                mod = lyd_mod_next_module(next, NULL, ctx, &i, &first);
             }
             if (!mod) {
                 break;