crypto: aegis128 - Fix -Wunused-const-variable warning

crypto/aegis.h:27:32: warning:
 crypto_aegis_const defined but not used [-Wunused-const-variable=]

crypto_aegis_const is only used in aegis128-core.c,
just move the definition over there.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>