ipmi: fix IPMI_SMI_MSG_TYPE_IPMB_DIRECT response length checking

A couple of issues:

The tested data sizes are wrong; during the design that changed and this
got missed.

The formatting of the reponse couldn't use the normal one, it has to be
an IPMB formatted response.

Reported-by: Jakub Kicinski <kuba@kernel.org>
Fixes: 059747c2 ("ipmi: Add support for IPMB direct messages")
Signed-off-by: Corey Minyard <cminyard@mvista.com>