crypto: aspeed - Fix dma_unmap_sg() direction

It seems like everywhere in this file, when the request is not
bidirectionala, req->src is mapped with DMA_TO_DEVICE and req->dst is
mapped with DMA_FROM_DEVICE.

Fixes: 62f58b16 ("crypto: aspeed - add HACE crypto driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>