crypto: ghash-clmulni-intel - Use u128 instead of be128 for internal key

The internal key isn't actually in big-endian format so let's switch
to u128 which also happens to allow us to remove a sparse warning.

Based on suggestion by Ard Biesheuvel.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>