crypto: chacha20 - Use unaligned access macros when loading key and IV

The generic ChaCha20 implementation has a cra_alignmask of 3, which
ensures that the key passed into crypto_chacha20_setkey() and the IV
passed into crypto_chacha20_init() are 4-byte aligned.  However, these
functions are also called from the ARM and ARM64 implementations of
ChaCha20, which intentionally do not have a cra_alignmask set.  This is
broken because 32-bit words are being loaded from potentially-unaligned
buffers without the unaligned access macros.

Fix it by using the unaligned access macros when loading the key and IV.

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