nouveau: fix a "can return -1 to userland" problem.

nvkm_ioctl_del() for some reason converts 0 into 1 return.  this
appears to be a way to avoid having a log printed by nvkm_ioctl()
and to trigger some dead code ("hack" is always NULL afaict.)
after consuming this value convert it back to 0 for ioctl return.


diff --git a/sys/external/bsd/drm2/dist/drm/nouveau/nvkm/core/nouveau_nvkm_core_ioctl.c b/sys/external/bsd/drm2/dist/drm/nouveau/nvkm/core/nouveau_nvkm_core_ioctl.c
index 213808ce46d4..47fbca2776a7 100644
--- a/sys/external/bsd/drm2/dist/drm/nouveau/nvkm/core/nouveau_nvkm_core_ioctl.c
+++ b/sys/external/bsd/drm2/dist/drm/nouveau/nvkm/core/nouveau_nvkm_core_ioctl.c
@@ -487,6 +487,10 @@ nvkm_ioctl(struct nvkm_client *client, bool supervisor,
 			client->data = NULL;
 		}
 	}
+#ifdef __NetBSD__
+	else
+		ret = 0;
+#endif
 
 	return ret;
 }