drm/amdgpu: fix random data corruption for sdma 7

There is random data corruption caused by const fill, this is caused by
write compression mode not correctly configured.

So correct compression mode for const fill.

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