crypto: inside-secure - do not access buffers mapped to the device

This patches update the way the digest is copied from the state buffer
to the result buffer, so that the copy only happen after the state
buffer was DMA unmapped, as otherwise the buffer would be owned by the
device.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>