vdsmapi-schema: fix typo in tpm device

Small typo in documentation, VmTpmDeviceType is in no way related
to smartcard.

Change-Id: I38c616af488f0861e9357249c00c47271e033832
Signed-off-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28393
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>