drm/lima: fix sched context destroy

The drm sched entity must be flushed before finishing, to account for
jobs potentially still in flight at that time.
Lima did not do this flush until now, so switch the destroy call to the
drm_sched_entity_destroy() wrapper which will take care of that.

This fixes a regression on lima which started since the rework in
commit 2fdb8a8f ("drm/scheduler: rework entity flush, kill and fini")
where some specific types of applications may hang indefinitely.

Fixes: 2fdb8a8f

 ("drm/scheduler: rework entity flush, kill and fini")
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606143247.433018-1-nunes.erico@gmail.com