drm/virtio: fix uninitialized variable

smatch reported this with the blob series:

drivers/gpu/drm/virtio/virtgpu_kms.c:227 virtio_gpu_init()
error: uninitialized symbol 'ret'.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20200902210847.2689-3-gurchetansingh@chromium.org


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>