cipher:dilithium: Fix the glue of libgcrypt.

* cipher/dilithium.h (dilithium_sign, dilithium_verify): Define the
macro correctly so that we can keep using _gcry namespace for internal
functions.

It was mistake when we followed the code of Kyber.

• Fixes-commit: 81a8332963e2a5581ee0e7d0393363e8b9015bbf
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>