fio HOWTO/man fix

If I use ioengine=cpu , fio errors out, I referred HOWTO and man pages,
both  says use "cpu" for cpu load. Looked at the code it should be
ioengine=cpuio.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.1 b/fio.1
index 2f60b5e..aacee10 100644
--- a/fio.1
+++ b/fio.1
@@ -244,7 +244,7 @@
 Like \fBnet\fR, but uses \fIsplice\fR\|(2) and \fIvmsplice\fR\|(2) to map data
 and send/receive.
 .TP
-.B cpu
+.B cpuio
 Doesn't transfer any data, but burns CPU cycles according to \fBcpuload\fR and
 \fBcpucycles\fR parameters.
 .TP