cipher: Fix return type of _gcry_ecc_mul_point.
* cipher/ecc-ecdh.c (_gcry_ecc_mul_point): Return gpg_err_code_t. * src/gcrypt-int.h (_gcry_ecc_mul_point): Return gpg_err_code_t. * src/visibility.c (gcry_ecc_mul_point): Follow the change.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>