test/ring: fix number of single element enqueue/dequeue
test/ring: fix number of single element enqueue/dequeue

The ring capacity is (RING_SIZE - 1), thus only (RING_SIZE - 1) number of
elements can be enqueued into the ring.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Feifei Wang <2493857810266eaae720c9869c8b9d6ce45d3739@arm.com>
Reviewed-by: Ruifeng Wang <a548d51fbc42485a8ba807711a537e88c2b59dd2@arm.com>
Reviewed-by: Phil Yang <5a9b6465c065ff0e1fd5d2cb9eb2185e82f34247@arm.com>
Reviewed-by: Honnappa Nagarahalli <01ccf438b971cc1d8919c8a7f18443cae9429d8b@arm.com>
Acked-by: Konstantin Ananyev <cbd5212b59ab42a210d72992d23a3aa17cfd3eaf@intel.com>

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