drm/virtio: remove ttm calls from in virtio_gpu_object_{reserve, unreserve}

Call reservation_object_* directly instead
of using ttm_bo_{reserve,unreserve}.

v4: check for EINTR only.
v3: check for EINTR too.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190829103301.3539-7-kraxel@redhat.com