error: add error_get_class()

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
diff --git a/error.c b/error.c
index 648706a..2d34cde 100644
--- a/error.c
+++ b/error.c
@@ -64,6 +64,11 @@
     return (errp && *errp);
 }
 
+ErrorClass error_get_class(const Error *err)
+{
+    return err->err_class;
+}
+
 const char *error_get_pretty(Error *err)
 {
     return err->msg;