drm/panel: simple: fix osd070t1718_19ts sync drive edge

The panel datasheet says that the panel samples at falling edge, but
does not say anything about h/v sync signals. Testing shows that if the
sync signals are driven on falling edge, the picture on the panel will
be slightly shifted right.

Setting sync drive edge to the same as data drive edge fixes this issue.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114093950.4101-4-tomi.valkeinen@ti.com