monitor: allow "help" show message for single command in sub group

A new parameter type 'S' is introduced to allow user input any string.
"help info block" works normal now.

Signed-off-by: Wenchao Xia <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Signed-off-by: Luiz Capitulino <[email protected]>
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 8c6b91a..c161fe9 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -11,7 +11,7 @@
 
     {
         .name       = "help|?",
-        .args_type  = "name:s?",
+        .args_type  = "name:S?",
         .params     = "[cmd]",
         .help       = "show the help",
         .mhandler.cmd = do_help_cmd,