Commit 7d79aa86 ("drm/vboxvideo: Replace struct vram_framebuffer
with generic implemenation") removed the diy framebuffer code from
the vboxvideo driver, resulting in a nice cleanup.

But since the vboxvideo driver needs the generic dirty tracking code,
it's drm_mode_config_funcs.fb_create should be set to
drm_gem_fb_create_with_dirty not drm_gem_fb_create.

This commit fixes this, fixing the framebuffer not always updating.

Cc: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 7d79aa86 ("drm/vboxvideo: Replace struct vram_framebuffer with generic implemenation")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20191028133159.236550-1-hdegoede@redhat.com