Return value of a function 'rte_zmalloc' is dereferenced without
checking, and it may call segmentation fault.

This patch fixed it.

Fixes: f8be1786b1b8 ("app/crypto-perf: introduce performance test
application")
Cc: stable@dpdk.org

Signed-off-by: Min Hu (Connor) <redacted>
---
v3:
* fix compiling warning.

Applied to dpdk-next-crypto

Thanks.