drm/v3d: Handle error from drm_sched_entity_init()

drm/v3d: Handle error from drm_sched_entity_init()

drm_sched_entity_init() can fail but its return value is currently being
ignored in v3d_open(). Check the return value and properly unwind
on failure by destroying any already-initialized scheduler entities.

Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patch.msgid.link/20260306-v3d-reset-locking-improv-v3-1-49864fe00692@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>