app/test: avoid freeing mbuf twice
app/test: avoid freeing mbuf twice

In cryptodev tests, when input and output buffers were the same,
the mbuf was being freed twice, causing refcnt_atomic to be negative.

Fixes: 202d375c60bc ("app/test: add cryptodev unit and performance tests")

Signed-off-by: Pablo de Lara <28355d9cfe41bb8148aea0fb24f47aae8f4217a1@intel.com>

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