drm/amdgpu: only move pt bos in LRU list on success

drm/amdgpu: only move pt bos in LRU list on success

BugLink: http://bugs.launchpad.net/bugs/1546572
This fixes a race condition in the error case: since the pt bos have not
necessarily been reserved in case of an error, we could move a pt bo that
is currently in the middle of being evicted/moved by another process,
which then resulted in a BUG_ON in ttm_bo_add_to_lru.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 28b8d66e0c1cc6c02b8159ae44aec359e12feefa)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>