drm/amdgpu: Use the sched from entity for amdgpu_cs trace

The problem is that base sched hasn't been assigned yet at this moment,
causing something like "ring=0" all the time from trace.

mpv:cs0-3473    [002] ..... 129.047431: amdgpu_cs: ring=0, dw=48, fences=0
mpv:cs0-3473    [002] ..... 129.089125: amdgpu_cs: ring=0, dw=48, fences=0
mpv:cs0-3473    [002] ..... 129.130987: amdgpu_cs: ring=0, dw=48, fences=0
mpv:cs0-3473    [002] ..... 129.172478: amdgpu_cs: ring=0, dw=48, fences=0

Fixes: 4624459c ("drm/amdgpu: add gang submit frontend v6")
Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>