drm/amdgpu/vcn:Remove bit 31 for scratch2 to indicate the WA is active

Remove bit 31 for scratch2 to indicate the Hardware bug work around is active.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>