UPSTREAM: drm/virtio: use u64_to_user_ptr macro

Other DRM drivers use it too.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190604234428.23252-1-gurchetansingh@chromium.org


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 4b013bb2d3a4a3104360746d2326d1408d179e72)
Signed-off-by: Greg Hartman <ghartman@google.com>
BUG: 139386237
Change-Id: Ide0a298304b5ad0fbbd15130b96376b4303b84e5