drm/omap: Remove duplicate calls to .set_timings() operation

The omap_dss_device .set_timings() operations are called directly from
omap_encoder_update(), and indirectly from the omap_dss_device .enable()
operation. The latter is called from omap_encoder_enable(), right after
calling omap_encoder_update(). The .set_timings() operation it thus
called twice in a row. Fix it by removing the indirect call.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>