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/HOWTO b/HOWTO
index d185f8a..5d757b2 100644
--- a/HOWTO
+++ b/HOWTO
@@ -347,7 +347,7 @@
 			netsplice Like net, but uses splice/vmsplice to
 				map data and send/receive.
 
-			cpu	Doesn't transfer any data, but burns CPU
+			cpuio	Doesn't transfer any data, but burns CPU
 				cycles according to the cpuload= and
 				cpucycle= options. Setting cpuload=85
 				will cause that job to do nothing but burn