test-dpif-dpdk: fix compilation warning message

Ring enqueue/deque functions were called with wrong arg type.

Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>
Reviewed-by: Meghan Halton <meghan.halton@intel.com>
Signed-off-by: Nicolas Pernas Maradei <nicolasx.pernas.maradei@intel.com>
Change-Id: I09b7881481a94f75bc5c438202992e5a9e7500ec