drm/sched: Fix kernel-doc warning for drm_sched_job_done()

drm/sched: Fix kernel-doc warning for drm_sched_job_done()

There is a kernel-doc warning for the scheduler:

Warning: drivers/gpu/drm/scheduler/sched_main.c:367 function parameter 'result' not described in 'drm_sched_job_done'

Fix the warning by describing the undocumented error code.

Fixes: 539f9ee4b52a ("drm/scheduler: properly forward fence errors")
Signed-off-by: Yujie Liu <yujie.liu@intel.com>
[phasta: Flesh out commit message]
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patch.msgid.link/20260227082452.1802922-1-yujie.liu@intel.com