examples/fips_validation: fix resetting pointer
examples/fips_validation: fix resetting pointer

The env.digest memory was freed, but the pointer was not set to NULL
afterwards. This caused an "Invalid Memory" error, as the pointer tries
to free twice.

Fixes: 952e10cdad5e ("examples/fips_validation: support scatter gather list")
Cc: stable@dpdk.org

Signed-off-by: Ciara Power <2dd8f648091a527a3f34edd30b226be01da76a0e@intel.com>
Acked-by: Fan Zhang <b46d470dc79aa6fd718cd24d07380f6203b7fc3c@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk