vDPA: fix 'cast to restricted le16' warnings in vdpa.c

This commit fixes spars warnings: cast to restricted __le16
in function vdpa_dev_net_config_fill() and
vdpa_fill_stats_rec()

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Message-Id: <20220722115309.82746-7-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>