drm/nouveau: Fix a couple of sparse warnings.

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
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 69c76cf..791531b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_gem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
@@ -577,7 +577,7 @@
 	struct drm_nouveau_gem_pushbuf_bo *bo;
 	struct nouveau_channel *chan;
 	struct validate_op op;
-	struct nouveau_fence *fence = 0;
+	struct nouveau_fence *fence = NULL;
 	int i, j, ret = 0, do_reloc = 0;
 
 	NOUVEAU_CHECK_INITIALISED_WITH_RETURN;