drm/nouveau/core/client: Mark nvkm_uclient_sclass with static keyword

Fix the following sparse warning:

drivers/gpu/drm/nouveau/nvkm/core/client.c:64:1: warning: symbol 'nvkm_uclient_sclass' was not declared. Should it be static?
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10

drivers/gpu/drm/nouveau/nvkm/core/client.c

@@ -60,7 +60,7 @@ nvkm_uclient_new(const struct nvkm_oclass *oclass, void *argv, u32 argc,
 	return 0;
 }
 
-const struct nvkm_sclass
+static const struct nvkm_sclass
 nvkm_uclient_sclass = {
 	.oclass = NVIF_CLASS_CLIENT,
 	.minver = 0,