On big endian arm64 kernels, the xchacha20-neon and xchacha12-neon
self-tests fail because hchacha_block_neon() outputs little endian words
but the C code expects native endianness.  Fix it to output the words in
native endianness (which also makes it match the arm32 version).

Fixes: cc7cf991 ("crypto: arm64/chacha20 - add XChaCha20 support")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>