drm/v3d: Checking for NULL vs IS_ERR()

The v3d_fence_create() only returns error pointers on error.  It never
returns NULL.

Fixes: 57692c94 ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180518081041.GC28335@mwanda

drivers/gpu/drm/v3d/v3d_sched.c

@@ -114,8 +114,8 @@ static struct dma_fence *v3d_job_run(struct drm_sched_job *sched_job)
 	v3d_invalidate_caches(v3d);
 
 	fence = v3d_fence_create(v3d, q);
-	if (!fence)
-		return fence;
+	if (IS_ERR(fence))
+		return NULL;
 
 	if (job->done_fence)
 		dma_fence_put(job->done_fence);