crypto: ecdh - comply with crypto_kpp_maxsize()

crypto_kpp_maxsize() asks for the output buffer size without
caring for errors. It allways assume that will be called after
a valid setkey. Comply with it and return what he wants.

nbytes has no sense now, remove it and directly return the maxsize.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ecdh.c

@@ -104,13 +104,12 @@ static int ecdh_compute_value(struct kpp_request *req)
 	return ret;
 }
 
-static int ecdh_max_size(struct crypto_kpp *tfm)
+static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 {
 	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
-	int nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 
-	/* Public key is made of two coordinates */
-	return 2 * nbytes;
+	/* Public key is made of two coordinates, add one to the left shift */
+	return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 }
 
 static void no_exit_tfm(struct crypto_kpp *tfm)