[CRYPTO] rmd256: Fix endian issues

This patch fixes endian issues making rmd256 work
properly on big-endian machines.

Signed-off-by: Adrian-Ken Rueegsegger <rueegsegger@swiss-it.ch>
Acked-by: Sebastian Siewior <sebastian@breakpoint.cc>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>