vdpa-dev: add get_vhost() callback for vhost-vdpa device

vdpa-dev: add get_vhost() callback for vhost-vdpa device

Commit c255488d67 "virtio: add vhost support for virtio devices"
added the get_vhost() function, but it did not include vhost-vdpa devices.

So when I use the vdpa device and query the status of the vdpa device
with the x-query-virtio-status qmp command, since vdpa does not implement
vhost_get, it will cause qemu to crash.

Therefore, in order to obtain the status of the virtio device under vhost-vdpa,
we need to add a vhost_get implement for the vdpa device.

Co-developed-by: Miao Kezhan <miaokezhan@baidu.com>
Signed-off-by: Miao Kezhan <miaokezhan@baidu.com>
Signed-off-by: Li Zhaoxin <lizhaoxin04@baidu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <2778f817cb6740a15ecb37927804a67288b062d1.1758860411.git.lizhaoxin04@baidu.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>