drm/amdgpu: correct doorbell range/size value for CSDMA_DOORBELL_RANGE

current function mixes CSDMA_DOORBELL_RANGE and SDMA0_DOORBELL_RANGE
range/size manipulation, while these 2 registers have difference size
field mask. Remove range/size manipulation for SDMA0_DOORBELL_RANGE.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Xiaojian Du <Xiaojian.Du@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>