OMAP: DSS2: Fix error path in omap_dsi_update()

In the case of an error on calling dsi_update_screen_l4(), a
successful framedone callback is still sent to panel-taal. An
error should be returned to taal_update() instead.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>