renamed OT::cff to OT::cff1 for consistency

along with HB_OT_TAG_cff1
diff --git a/src/hb-subset.cc b/src/hb-subset.cc
index 98401a4..bf9c399 100644
--- a/src/hb-subset.cc
+++ b/src/hb-subset.cc
@@ -272,8 +272,8 @@
     case HB_OT_TAG_post:
       result = _subset<const OT::post> (plan);
       break;
-    case HB_OT_TAG_cff:
-      result = _subset<const OT::cff> (plan);
+    case HB_OT_TAG_cff1:
+      result = _subset<const OT::cff1> (plan);
       break;
     case HB_OT_TAG_cff2:
       result = _subset<const OT::cff2> (plan);