crypto: skcipher - Fix -Wstringop-truncation warnings

crypto: skcipher - Fix -Wstringop-truncation warnings

As of GCC 9.0.0 the build is reporting warnings like:

    crypto/ablkcipher.c: In function ‘crypto_ablkcipher_report’:
    crypto/ablkcipher.c:374:2: warning: ‘strncpy’ specified bound 64 equals destination size [-Wstringop-truncation]
      strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: "<default>",
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       sizeof(rblkcipher.geniv));
       ~~~~~~~~~~~~~~~~~~~~~~~~~

This means the strnycpy might create a non null terminated string.  Fix this by
explicitly performing '\0' termination.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Nick Desaulniers <nick.desaulniers@gmail.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>