tpm: Use EMSGSIZE instead of EBADMSG to compile on OpenBSD

EBADMSG was only added to OpenBSD very recently. To make QEMU compilable
on older OpenBSD versions use EMSGSIZE instead when a mismatch between
number of received bytes and message size indicated in the header was
found.

Return -EMSGSIZE and convert all other errnos in the same functions to
return the negative errno.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
