drm/amdgpu: fix RAS unload driver issue in SRIOV

Fix null pointer issue when unload driver in SRIOV mode.

Adjust the function position to ensure that the amdgpu_mca/aca_xxx_init()
related functions can be initialized properly.

Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>