[media] omap3isp: Move setting constaints above media_entity_pipeline_start

The clock rate for l3_ick will soon be read during pipeline validation which
is now part of media_entity_pipeline_start(). For that reason we set
constraints earlier on.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>