drm/amdgpu: stop data_exchange work thread before reset

In FLR routine, init_data_exchange is called at reset_sriov
while fini_data_exchange is not. This will duplicating work
thread.

So call fini_data_exchange before reset for SRIOV

Signed-off-by: Tiecheng Zhou <Tiecheng.Zhou@amd.com>
Signed-off-by: Bokun Zhang <Bokun.Zhang@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>