drm/scheduler: quieten kernel-doc warnings

Fix kernel-doc warnings in gpu_scheduler.h and sched_main.c.

Quashes these warnings:

include/drm/gpu_scheduler.h:332: warning: missing initial short description on line:
 * struct drm_sched_backend_ops
include/drm/gpu_scheduler.h:412: warning: missing initial short description on line:
 * struct drm_gpu_scheduler
include/drm/gpu_scheduler.h:461: warning: Function parameter or member 'dev' not described in 'drm_gpu_scheduler'

drivers/gpu/drm/scheduler/sched_main.c:201: warning: missing initial short description on line:
 * drm_sched_dependency_optimized
drivers/gpu/drm/scheduler/sched_main.c:995: warning: Function parameter or member 'dev' not described in 'drm_sched_init'

Fixes: 2d33948e ("drm/scheduler: add documentation")
Fixes: 8ab62eda ("drm/sched: Add device pointer to drm_gpu_scheduler")
Fixes: 542cff78 ("drm/sched: Avoid lockdep spalt on killing a processes")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Cc: Nayan Deshmukh <nayan26deshmukh@gmail.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Jiawei Gu <Jiawei.Gu@amd.com>
Cc: dri-devel@lists.freedesktop.org
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220404213040.12912-1-rdunlap@infradead.org