crypto: atmel-aes - correct usage of dma_sync_* API

The output buffer is used for CPU access, so
the API should be dma_sync_single_for_cpu which
makes the cache line invalid in order to reload
the value in memory.

Signed-off-by: Leilei Zhao <leilei.zhao@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>