crypto: chacha20 - Fix unaligned access when loading constants

The four 32-bit constants for the initial state of ChaCha20 were loaded
from a char array which is not guaranteed to have the needed alignment.

Fix it by just assigning the constants directly instead.

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>