crypto: lrw - use correct alignmask

Commit c778f96b ("crypto: lrw - Optimize tweak computation")
incorrectly reduced the alignmask of LRW instances from
'__alignof__(u64) - 1' to '__alignof__(__be32) - 1'.

However, xor_tweak() and setkey() assume that the data and key,
respectively, are aligned to 'be128', which has u64 alignment.

Fix the alignmask to be at least '__alignof__(be128) - 1'.

Fixes: c778f96b ("crypto: lrw - Optimize tweak computation")
Cc: <stable@vger.kernel.org> # v4.20+
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>