crypto: morus/generic - fix for big endian systems

Omit the endian swabbing when folding the lengths of the assoc and
crypt input buffers into the state to finalize the tag. This is not
necessary given that the memory representation of the state is in
machine native endianness already.

This fixes an error reported by tcrypt running on a big endian system:

  alg: aead: Test 2 failed on encryption for morus640-generic
  00000000: a8 30 ef fb e6 26 eb 23 b0 87 dd 98 57 f3 e1 4b
  00000010: 21
  alg: aead: Test 2 failed on encryption for morus1280-generic
  00000000: 88 19 1b fb 1c 29 49 0e ee 82 2f cb 97 a6 a5 ee
  00000010: 5f

Fixes: 396be41f ("crypto: morus - Add generic MORUS AEAD implementations")
Cc: <stable@vger.kernel.org> # v4.18+
Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>