drm/exynos: g2d: fix missing unlock on error in g2d_runqueue_worker()

Add the missing unlock before return from function g2d_runqueue_worker()
in the error handling case.

Fixes: 445d3bed ("drm/exynos: use pm_runtime_resume_and_get()")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -897,13 +897,14 @@ static void g2d_runqueue_worker(struct work_struct *work)
 			ret = pm_runtime_resume_and_get(g2d->dev);
 			if (ret < 0) {
 				dev_err(g2d->dev, "failed to enable G2D device.\n");
-				return;
+				goto out;
 			}
 
 			g2d_dma_start(g2d, g2d->runqueue_node);
 		}
 	}
 
+out:
 	mutex_unlock(&g2d->runqueue_mutex);
 }