vdpa: Fix file descriptor leak on get features error

File descriptor vdpa_device_fd is not free in the case of returning
error from vhost_vdpa_get_features. Fixing it by making all errors go to
the same error path.

Resolves: Coverity CID 1490785
Fixes: 8170ab3f ("vdpa: Extract get features part from vhost_vdpa_get_max_queue_pairs")

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220802112447.249436-2-eperezma@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>