drm/panfrost: Make ->run_job() return an ERR_PTR() when appropriate

If the fence creation fail, we can return the error pointer directly.
The core will update the fence error accordingly.
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210630062751.2832545-4-boris.brezillon@collabora.com

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -344,7 +344,7 @@ static struct dma_fence *panfrost_job_run(struct drm_sched_job *sched_job)
 
 	fence = panfrost_fence_create(pfdev, slot);
 	if (IS_ERR(fence))
-		return NULL;
+		return fence;
 
 	if (job->done_fence)
 		dma_fence_put(job->done_fence);