dss_mgr_wait_for_vsync() uses dssdev->type to find out if the output is
going to VENC, HDMI, or something else. This creates a dependency on
dssdev, which we want to remove. The task is more logically done by
looking at the output to which the overlay manager in question is
connected to.

This patch changes the code to use output->id to find out which kind of
output we use.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Archit Taneja <archit@ti.com>