crypto: caam - create ahash shared descriptors only once

For keyed hash algorithms, shared descriptors are currently generated
twice:
-at tfm initialization time, in cra_init() callback
-in setkey() callback

Since it's mandatory to call setkey() for keyed algorithms, drop the
generation in cra_init().

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>