mempool: fix leak if populate fails

This patch fixes the issue of memzone not being freed incase the
rte_mempool_populate_phys fails in the rte_mempool_populate_default

This issue was identified when testing with OVS ~2.6
- configure the system with low memory (e.g. < 500 MB)
- add bridge and dpdk interfaces
- delete brigde
- keep on repeating the above sequence.

Fixes: d1d914ebbc25 ("mempool: allocate in several memory chunks by default")

Signed-off-by: Nipun Gupta <nipun.gupta@nxp.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>