Correct callback arg type

mpi/src/mpi_failure_tolerance/starpu_mpi_checkpoint_template.c

@@ -182,8 +182,8 @@ static starpu_mpi_checkpoint_template_t _starpu_mpi_get_checkpoint_template_by_i
 void checkpoint_discard(void* _args)
 {
 	// TODO: flag data as "CP ready", since the CP has succeeded
-	struct _starpu_mpi_cp_ack_msg* message = (struct _starpu_mpi_cp_ack_msg*) _args;
-	fprintf(stderr, "DISCARDING OLD CHECKPOINT DATA - new one is CPID:%d - CPINST:%d\n", message->checkpoint_id, message->checkpoint_instance);
+	struct _starpu_mpi_cp_discard_arg_cb* arg = (struct _starpu_mpi_cp_discard_arg_cb*) _args;
+	fprintf(stderr, "DISCARDING OLD CHECKPOINT DATA - new one is CPID:%d - CPINST:%d\n", arg->msg.checkpoint_id, arg->msg.checkpoint_instance);
 }
 
 int _starpu_mpi_checkpoint_post_cp_discard_recv(starpu_mpi_checkpoint_template_t cp_template)