drm/omap: panel-tpo-td028ttec1: Add note for incorrect sync drive edge

According to the datasheet of the panel, both data, DEN and sync signals
are expected to be driven on the falling edge of the DOTCLK.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>