sunxi: video: Fix lvds panel support for sun6i+

We've never tested the lvds panel support on sun6i+ SoCs until now, and
unsurprisingly the lvds code needed some fixes to work on my ga10h A33
tablet with lvds panel. This makes the panel on that tablet actually work.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>