crypto: cavium/nitrox - fix warnings while printing atomic64_t types

fix compilation warnings with nitrox_debugfs.c while printing
atomic64_t types on arm64. typecast the atomic64_read() value to u64

This issue is reported by Ard Biesheuvel

drivers/crypto/cavium/nitrox/nitrox_debugfs.c:62:30:
warning: format ‘%lld’ expects argument of type ‘long long int’,
         but argument 3 has type ‘long int’ [-Wformat=]
  seq_printf(s, "  Posted: %lld\n", atomic64_read(&ndev->stats.posted));
                              ^
Fixes: 2a8780be (crypto: cavium/nitrox - updated debugfs information)
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Srikanth Jampala <Jampala.Srikanth@cavium.com>
Reviewed-by: Gadam Sreerama <sgadam@cavium.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>