drm/exynos: consider common clock framework to g2d driver.

This patch just changes clk_enable/disable to
clk_prepare_enable/clk_disable_unprepare, and
adds related exception codes.
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -806,9 +806,20 @@ static void g2d_dma_start(struct g2d_data *g2d,
 	struct g2d_cmdlist_node *node =
 				list_first_entry(&runqueue_node->run_cmdlist,
 						struct g2d_cmdlist_node, list);
+	int ret;
+
+	ret = pm_runtime_get_sync(g2d->dev);
+	if (ret < 0) {
+		dev_warn(g2d->dev, "failed pm power on.\n");
+		return;
+	}
 
-	pm_runtime_get_sync(g2d->dev);
-	clk_enable(g2d->gate_clk);
+	ret = clk_prepare_enable(g2d->gate_clk);
+	if (ret < 0) {
+		dev_warn(g2d->dev, "failed to enable clock.\n");
+		pm_runtime_put_sync(g2d->dev);
+		return;
+	}
 
 	writel_relaxed(node->dma_addr, g2d->regs + G2D_DMA_SFR_BASE_ADDR);
 	writel_relaxed(G2D_DMA_START, g2d->regs + G2D_DMA_COMMAND);
@@ -861,7 +872,7 @@ static void g2d_runqueue_worker(struct work_struct *work)
 					    runqueue_work);
 
 	mutex_lock(&g2d->runqueue_mutex);
-	clk_disable(g2d->gate_clk);
+	clk_disable_unprepare(g2d->gate_clk);
 	pm_runtime_put_sync(g2d->dev);
 
 	complete(&g2d->runqueue_node->complete);