drm/amdkfd: Use better name for sdma queue non HWS path

The old name is prone to confusion. The register offset is for a RLC queue
rather than a SDMA engine. The value is not a base address, but a
register offset.

Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>