drm/panthor: Fix a leak when a group is evicted before the tiler OOM is serviced

drm/panthor: Fix a leak when a group is evicted before the tiler OOM is serviced

A group ref is tied to the pending tiler_oom_work, so we need to release
it if the cancel was effective.

Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260623-panthor-signal-from-irq-v3-0-2ece396f8ee0@collabora.com?part=7
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260625-panthor-misc-fixes-v1-9-b67ed973fea6@collabora.com