REG3 no longer needs to be updated, since it's not used after that.
This shared descriptor command is a leftover of the conversion to
AEAD interface.

Fixes: 479bcc7c "crypto: caam - Convert authenc to new AEAD interface"
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>