crypto: dh - update test for public key verification

By adding a zero byte-length for the DH parameter Q value, the public
key verification test is disabled for the given test.

Reported-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>