crypto: x86/ghash - fix unaligned access in ghash_setkey()

The key can be unaligned, so use the unaligned memory access helpers.

Fixes: 8ceee728

 ("crypto: ghash-clmulni-intel - use C implementation for setkey()")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>