drm/amdgpu: fix sdma v4 init microcode error

Fix init SDMA microcode error for sdma v4, which caused by mistake when
rearch sdma init microcode function (coding 4.2.2 to 4.2.0).

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>