drm/scheduler: Fix job cleanup without timeout handler

After "5918045c drm/scheduler: rework job destruction", jobs are
only deleted when the timeout handler is able to be cancelled
successfully.

In case no timeout handler is running (timeout == MAX_SCHEDULE_TIMEOUT),
job cleanup would be skipped which may result in memory leaks.

Add the handling for the (timeout == MAX_SCHEDULE_TIMEOUT) case in
drm_sched_cleanup_jobs.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/306025/?series=60878&rev=2