[HIFN]: Have HW invalidate src and dest descriptors after processing

The descriptors need to be invalidated after processing for ring
cleanup to work properly and to avoid using an old destination
descriptor when the src and cmd descriptors are already set up
and the dst descriptor isn't.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>