We were doing backlog notification callbacks via a cipher/hash/aead
request structure cast to the base structure, which may or may not
work based on how the structure is laid in memory and is not safe.

Fix it by delegating the backlog notification to the appropriate
internal callbacks which are type aware.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>