drm/amdgpu: toggle on DF Cstate after finishing xgmi injection

Fixes: 5c23e9e0 ("drm/amdgpu: Update RAS XGMI error inject sequence")
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>