drm/scheduler: fix documentation by replacing rq_list with sched_list

This also replaces old artifacts with a correct one in drm_sched_entity_init()
declaration

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>