drm/panel: simple: fix vertical timings for Innolux AT043TN24

The vsync length should be 10 lines, as specified in the data sheet.
This gets the actual refresh rate closer to nominal 60 Hz given the
9 MHz pixel clock.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171011125958.23064-1-p.zabel@pengutronix.de