crypto: qat: fix issue when mapping assoc to internal AD struct

This patch fixes an issue when building an internal AD representation.
We need to check assoclen and not only blindly loop over assoc sgl.

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>