test/mempool_perf: free mempool on exit
test/mempool_perf: free mempool on exit

Mempool_perf test not freeing pool memory.

Signed-off-by: Santosh Shukla <23b682afe3504ae4f88c66c3cabfb34f87e9916e@caviumnetworks.com>
Acked-by: Shreyansh Jain <9744844f062a9f6cf95f66f06508da54c8fc7929@nxp.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

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