crypto: iaa - fix the missing CRYPTO_ALG_ASYNC in cra_flags

Add the missing CRYPTO_ALG_ASYNC flag since intel iaa driver
works asynchronously.

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>