drm/panthor: Report group as timedout when we fail to properly suspend

If we don't do that, the group is considered usable by userspace, but
all further GROUP_SUBMIT will fail with -EINVAL.

Changes in v3:
- Add R-bs

Changes in v2:
- New patch

Fixes: de854881 ("drm/panthor: Add the scheduler logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029152912.270346-3-boris.brezillon@collabora.com