[subset-cff] Fix previous commit

Oops!

src/hb-subset-cff-common.hh

@@ -118,7 +118,7 @@ struct str_encoder_t
       set_error ();
       return;
     }
-    memcpy (&buff.arrayZ + offset, &str[0], str.length);
+    memcpy (buff.arrayZ + offset, &str[0], str.length);
   }
 
   bool is_error () const { return error; }