drm/nouveau: wrap calls to ttm_bo_validate()

This will be used later to fixup bo.offset with a buffer's fixed GPU
virtual address.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
index 9886b64..0adb2a8 100644
--- a/drivers/gpu/drm/nouveau/nouveau_gem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
@@ -358,8 +358,7 @@
 		}
 
 		nvbo->channel = (b->read_domains & (1 << 31)) ? NULL : chan;
-		ret = ttm_bo_validate(&nvbo->bo, &nvbo->placement,
-				      true, false, false);
+		ret = nouveau_bo_validate(nvbo, true, false, false);
 		nvbo->channel = NULL;
 		if (unlikely(ret)) {
 			if (ret != -ERESTARTSYS)