refs: use designated initializers for "struct ref_iterator_vtable"

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs/files-backend.c b/refs/files-backend.c
index f95552f..aa4e718 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -822,9 +822,9 @@ static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
 }
 
 static struct ref_iterator_vtable files_ref_iterator_vtable = {
-	files_ref_iterator_advance,
-	files_ref_iterator_peel,
-	files_ref_iterator_abort
+	.advance = files_ref_iterator_advance,
+	.peel = files_ref_iterator_peel,
+	.abort = files_ref_iterator_abort,
 };
 
 static struct ref_iterator *files_ref_iterator_begin(
@@ -2231,9 +2231,9 @@ static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
 }
 
 static struct ref_iterator_vtable files_reflog_iterator_vtable = {
-	files_reflog_iterator_advance,
-	files_reflog_iterator_peel,
-	files_reflog_iterator_abort
+	.advance = files_reflog_iterator_advance,
+	.peel = files_reflog_iterator_peel,
+	.abort = files_reflog_iterator_abort,
 };
 
 static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,