ethdev: explicit cast of queue count return

ethdev: explicit cast of queue count return

GCC 8.1 produces a warning:
rte_ethdev.h: In function 'rte_eth_rx_queue_count':
rte_ethdev.h:3882:10: warning: conversion to 'int' from 'uint32_t'
{aka 'unsigned int'} may change the sign of the result [-Wsign-conversion]
  return (*dev->dev_ops->rx_queue_count)(dev, queue_id);
         ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 33cf6be04d60 ("ethdev: add sanity checks to functions")
Cc: stable@dpdk.org
Signed-off-by: Andy Green <andy@warmcat.com>