help: Fix markup of heading "USB options" so it appears in -help

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1360781383-28635-6-git-send-email-armbru@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 8c435cd..ce9602f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -538,9 +538,10 @@
 STEXI
 @end table
 ETEXI
+DEFHEADING()
 
+DEFHEADING(USB options:)
 STEXI
-USB options:
 @table @option
 ETEXI