crypto: hisilicon/sec2 - fix for aead auth key length

According to the HMAC RFC, the authentication key
can be 0 bytes, and the hardware can handle this
scenario. Therefore, remove the incorrect validation
for this case.

Fixes: 2f072d75 ("crypto: hisilicon - Add aead support on SEC2")
Signed-off-by: Wenkai Lin <linwenkai6@hisilicon.com>
Signed-off-by: Chenghai Huang <huangchenghai2@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>