crypto: mips/chacha - select CRYPTO_SKCIPHER, not CRYPTO_BLKCIPHER

Another instance of CRYPTO_BLKCIPHER made it in just after it was
renamed to CRYPTO_SKCIPHER.  Fix it.

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