crypto: dh - return unsigned value for crypto_dh_key_len()

DH_KPP_SECRET_MIN_SIZE and dh_data_size() are both returning
unsigned values.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/include/crypto/dh.h b/include/crypto/dh.h
index f638998..71e1bb2 100644
--- a/include/crypto/dh.h
+++ b/include/crypto/dh.h
@@ -53,7 +53,7 @@ struct dh {
  *
  * Return: size of the key in bytes
  */
-int crypto_dh_key_len(const struct dh *params);
+unsigned int crypto_dh_key_len(const struct dh *params);
 
 /**
  * crypto_dh_encode_key() - encode the private key