drm/etnaviv: don't put fence in case of submit failure

If we bail out of the submit before actually adding the cmdstream
to the kernel ring there is no valid fence to put. Make sure to skip
the fence_put in that case.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c

@@ -44,6 +44,7 @@ static struct etnaviv_gem_submit *submit_create(struct drm_device *dev,
 
 		/* initially, until copy_from_user() and bo lookup succeeds: */
 		submit->nr_bos = 0;
+		submit->fence = NULL;
 
 		ww_acquire_init(&submit->ticket, &reservation_ww_class);
 	}
@@ -294,7 +295,8 @@ static void submit_cleanup(struct etnaviv_gem_submit *submit)
 	}
 
 	ww_acquire_fini(&submit->ticket);
-	dma_fence_put(submit->fence);
+	if (submit->fence)
+		dma_fence_put(submit->fence);
 	kfree(submit);
 }