crypto: crypto4xx - Call dma_unmap_page when done

In crypto4xx_cipher_done, we should be unmapping the dst page, not
mapping it.

This was flagged by a sparse warning about the unused addr variable.
While we're at it, also fix a sparse warning regarding the unused
ctx variable in crypto4xx_ahash_done (by actually using it).

Fixes: 049359d6

 ("crypto: amcc - Add crypt4xx driver")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>