drm/vc4: hvs: Fix dlist debug not resetting the next entry pointer

drm/vc4: hvs: Fix dlist debug not resetting the next entry pointer

The debug function to display the dlists didn't reset next_entry_start
when starting each display, so resulting in not stopping the
list at the correct place.

Fixes: c6dac00340fc ("drm/vc4: hvs: Add debugfs node that dumps the current display lists")
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240621152055.4180873-18-dave.stevenson@raspberrypi.com
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>