Fix cpumask setting/getting on older kernels

Don't call into the affinity functions, unless the user has
specified a mask.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/init.c b/init.c
index 0df30a2..355de88 100644
--- a/init.c
+++ b/init.c
@@ -655,10 +655,7 @@
 {
 	memset(&def_thread, 0, sizeof(def_thread));
 
-	if (fio_getaffinity(getpid(), &def_thread.o.cpumask) == -1) {
-		perror("sched_getaffinity");
-		return 1;
-	}
+	fio_getaffinity(getpid(), &def_thread.o.cpumask);
 
 	/*
 	 * fill default options