crypto: nx - remove unused variables 'nx_driver_string' and 'nx_driver_version'

drivers/crypto/nx/nx.h:12:19: warning:
 nx_driver_string defined but not used [-Wunused-const-variable=]
drivers/crypto/nx/nx.h:13:19: warning:
 nx_driver_version defined but not used [-Wunused-const-variable=]

They are never used, so just remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>