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>
diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index 3de2898..63ca337 100644
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -38,7 +38,8 @@ static unsigned int ecdh_supported_curve(unsigned int curve_id)
 	}
 }
 
-static int ecdh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
+static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
+			   unsigned int len)
 {
 	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 	struct ecdh params;