drm/nouveau: sched: fix leaking memory of timedout job

Always stop and re-start the scheduler in order to let the scheduler
free up the timedout job in case it got signaled. In case of exec jobs
the job type specific callback will take care to signal all fences and
tear down the channel.

Fixes: b88baab8

 ("drm/nouveau: implement new VM_BIND uAPI")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230916162835.5719-1-dakr@redhat.com