drm/amdgpu: fix bug of vm_bo_map (v2)

call reservation_object_reserve_shared before amdgpu_bo_fence

Signed-off-by: monk.liu <monk.liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jammy Zhou <jammy.zhou@amd.com>