Fix the wrong description in qemu manual

Fix LP#1151450 the wrong description in qemu manual:

'qemu-system-x86_84' should be 'qemu-system-x86_64'.
Signed-off-by: NLei Li <lilei@linux.vnet.ibm.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

qemu-options.hx

@@ -2132,7 +2132,7 @@ gluster[+transport]://[server[:port]]/volname/image[?socket=...]
 
 Example
 @example
-qemu-system-x86_84 --drive file=gluster://192.0.2.1/testvol/a.img
+qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img
 @end example
 
 See also @url{http://www.gluster.org}.