drm/amdgpu: Correct unlocked update fence handling

To fix two issues with unlocked update fence:

1. vm->last_unlocked store the latest fence without taking refcount.
2. amdgpu_vm_bo_update_mapping returns old fence, not the latest fence.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c

@@ -109,7 +109,7 @@ static int amdgpu_vm_sdma_commit(struct amdgpu_vm_update_params *p,
 	if (p->unlocked) {
 		struct dma_fence *tmp = dma_fence_get(f);
 
-		swap(p->vm->last_unlocked, f);
+		swap(p->vm->last_unlocked, tmp);
 		dma_fence_put(tmp);
 	} else {
 		amdgpu_bo_fence(p->vm->root.bo, f, true);