OMAPDSS: TPO-TD03MTEA1: update default gamma

Over time better gamma has been determined and tuned with some
equipment so update the defaults. From subjective point of view
dark shades should be better visible.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>