drm/panel: simple: Correct minimum hsync length of the HannStar HSD070PWW1 panel

According to the data sheet, the minimum horizontal blanking interval
is 54 clocks (1 + 52 + 1), but tests with a Nitrogen6X have shown the
minimum working horizontal blanking interval to be 60 clocks.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>