hash: fix position returned in free slots

hash: fix position returned in free slots

Currently, in rte_hash_free_key_with_position(), the position returned
to the ring of free_slots leads to an unexpected conflict with a key
already in use.

This patch fixes incorrect position returned to the ring of free_slots.

Bugzilla ID: 261
Fixes: 9d033dac7d7c ("hash: support no free on delete")
Cc: stable@dpdk.org
Reported-by: Linfan <zhongdahulinfan@163.com>
Suggested-by: Linfan <zhongdahulinfan@163.com>
Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Acked-by: Yipeng Wang <yipeng1.wang@intel.com>