CPU set creation and destruction can fail on some platforms

Check for that and error out if necessary.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index 2a468b1..30b40cc 100644
--- a/fio.c
+++ b/fio.c
@@ -1116,8 +1116,11 @@
 	close_ioengine(td);
 	cleanup_io_u(td);
 
-	if (td->o.cpumask_set)
-		fio_cpuset_exit(td);
+	if (td->o.cpumask_set) {
+		int ret = fio_cpuset_exit(&td->o.cpumask);
+
+		td_verror(td, ret, "fio_cpuset_exit");
+	}
 
 	/*
 	 * do this very late, it will log file closing as well