drm/vc4: hvs: Remove dlist setup duplication

Setting the DISPLISTx register needs to occur in every case, and we
don't need to protect the register using the event_lock, so we can just
move it after the if branches and simplify a bit the function.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220331143744.777652-5-maxime@cerno.tech