crypto: crc32c-generic - remove cra_alignmask

crc32c-generic sets an alignmask, but actually its ->update() works with
any alignment; only its ->setkey() and outputting the final digest
assume an alignment.  To prevent the buffer from having to be aligned by
the crypto API for just these cases, switch these cases over to the
unaligned access macros and remove the cra_alignmask.  Note that this
also makes crc32c-generic more consistent with crc32-generic.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>