cocci: apply the "cache.h" part of "the_repository.pending"

Apply the part of "the_repository.pending.cocci" pertaining to
"cache.h".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff-lib.c b/diff-lib.c
index dec040c..24470b2 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -581,7 +581,7 @@ void diff_get_merge_base(const struct rev_info *revs, struct object_id *mb)
 	if (revs->pending.nr == 1) {
 		struct object_id oid;
 
-		if (get_oid("HEAD", &oid))
+		if (repo_get_oid(the_repository, "HEAD", &oid))
 			die(_("unable to get HEAD"));
 
 		mb_child[1] = lookup_commit_reference(the_repository, &oid);