refs: update ref transactions to use struct object_id

Update the ref transaction code to use struct object_id.  Remove one
NULL pointer check which was previously inserted around a dereference;
since we now pass a pointer to struct object_id directly through, the
code we're calling handles this for us.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 225c734..859be91 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -457,8 +457,8 @@ static int s_update_ref(const char *action,
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref->name,
-				   ref->new_oid.hash,
-				   check_old ? ref->old_oid.hash : NULL,
+				   &ref->new_oid,
+				   check_old ? &ref->old_oid : NULL,
 				   0, msg, &err))
 		goto fail;