drm/nouveau: fix build with CONFIG_AGP=n

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 320a14b..aa2dfbc 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -311,8 +311,10 @@
 	struct drm_device *dev = dev_priv->dev;
 
 	switch (dev_priv->gart_info.type) {
+#if __OS_HAS_AGP
 	case NOUVEAU_GART_AGP:
 		return ttm_agp_backend_init(bdev, dev->agp->bridge);
+#endif
 	case NOUVEAU_GART_SGDMA:
 		return nouveau_sgdma_init_ttm(dev);
 	default: