crypto: starfive - Pad adata with zeroes

Aad requires padding with zeroes up to 15 bytes in some cases. This
patch increases the allocated buffer size for aad and prevents the
driver accessing uninitialized memory region.

v1->v2: Specify reason for alloc size change in descriptions.

Signed-off-by: Jia Jie Ho <jiajie.ho@starfivetech.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>