drm/panthor: Fail job creation when the group is dead

drm/panthor: Fail job creation when the group is dead

Userspace can use GROUP_SUBMIT errors as a trigger to check the group
state and recreate the group if it became unusable. Make sure we
report an error when the group became unusable.

Changes in v3:
- None

Changes in v2:
- Add R-bs

Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Signed-off-by: Boris Brezillon <[email protected]>
Reviewed-by: Steven Price <[email protected]>
Reviewed-by: Liviu Dudau <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]