tpm: report backend request error

Use an Error** for request to let the caller handle error reporting.

This will also allow to inform the frontend of a backend error.

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