drm/sched: Remove redundant check

The rq pointer points inside the drm_gpu_scheduler structure. Thus
it can't be NULL.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c61cdbdb ("drm/scheduler: Fix hang when sched_entity released")
Signed-off-by: Vladislav Efanov <VEfanov@ispras.ru>
Link: https://lore.kernel.org/r/20230517125247.434103-1-VEfanov@ispras.ru


Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>