drm/nouveau: only call ttm_agp_tt_create when __OS_HAS_AGP

ttm_agp_tt_create is itself defined under CONFIG_AGP, so there's no
point calling it otherwise.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -456,13 +456,15 @@ static struct ttm_tt *
 nouveau_ttm_tt_create(struct ttm_bo_device *bdev, unsigned long size,
 		      uint32_t page_flags, struct page *dummy_read)
 {
+#if __OS_HAS_AGP
 	struct nouveau_drm *drm = nouveau_bdev(bdev);
 	struct drm_device *dev = drm->dev;
 
 	if (drm->agp.stat == ENABLED) {
 		return ttm_agp_tt_create(bdev, dev->agp->bridge, size,
 					 page_flags, dummy_read);
 	}
+#endif
 
 	return nouveau_sgdma_create_ttm(bdev, size, page_flags, dummy_read);
 }