drm/amdgpu/sriov:fix page fault issue of driver unload

bo_free on csa is too late to put in amdgpu_fini because that
time ttm is already finished,
Move it earlier to avoid the page fault.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Horace Chen <horace.chen@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>