drm/amdgpu: drop setting buffer funcs in sdma442

To fix the entity rq NULL issue. This setting has been moved
to upper level.

Fixes: b7043800 ("drm/amdgpu: move buffer funcs setting up a level")
Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>