test/reorder: fix out of bound access

The value of array index 'i' is out of bound because of the previous
loop it has been used.

Assuming intention is using '0' since the check before free is robufs[0]
check, fixing according.

Fixes: ecd867faa8 ("test/reorder: fix freeing mbuf twice")
Cc: stable@dpdk.org

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>

test/test/test_reorder.c

@@ -269,7 +269,7 @@ test_reorder_drain(void)
 		goto exit;
 	}
 	if (robufs[0] != NULL)
-		rte_pktmbuf_free(robufs[i]);
+		rte_pktmbuf_free(robufs[0]);
 
 	/* Insert more packets
 	 * RB[] = {NULL, NULL, NULL, NULL}