crypto: kpp - constify buffer passed to crypto_kpp_set_secret()

Constify the buffer passed to crypto_kpp_set_secret() and
kpp_alg.set_secret, since it is never modified.

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

crypto/dh.c

@@ -79,7 +79,8 @@ static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
 	return 0;
 }
 
-static int dh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
+static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
+			 unsigned int len)
 {
 	struct dh_ctx *ctx = dh_get_ctx(tfm);
 	struct dh params;