drm/panthor: Relax a check in panthor_sched_pre_reset()

drm/panthor: Relax a check in panthor_sched_pre_reset()

Groups are only moved out of the runnable lists when
panthor_group_stop() is called or when they run out of jobs.
What should not happen though is having one group added to one of
the runnable list after reset.in_progress has been set to true, but
that's not something we can easily check, so let's just drop the
WARN_ON() in panthor_sched_pre_reset().

v2:
- Adjust explanation in commit message

v3:
- Collect R-b

v4:
- No changes

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251128084841.3804658-7-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>