app/crypto-perf: fix uninitialized values for null ops

app/crypto-perf: fix uninitialized values for null ops

Some values are uninitialized for "cipher null" and "auth null"
operations. It may cause unpredictable results for some crypto pmd
drivers, or even segmentation fault.

This patch sets values for null operations to zero.

Fixes: f8be1786b1b8 ("app/crypto-perf: introduce performance test application")
Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>