drm/nouveau/tegra: remove needless NULL check

There has already been NULL check in clk_prepare_enable() and
clk_disable_unprepare(), so remove needless NULL check before
calling them.
Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220519072950.128268-1-guozhengkui@vivo.com

drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c

@@ -41,11 +41,9 @@ nvkm_device_tegra_power_up(struct nvkm_device_tegra *tdev)
 	ret = clk_prepare_enable(tdev->clk);
 	if (ret)
 		goto err_clk;
-	if (tdev->clk_ref) {
 	ret = clk_prepare_enable(tdev->clk_ref);
 	if (ret)
 		goto err_clk_ref;
-	}
 	ret = clk_prepare_enable(tdev->clk_pwr);
 	if (ret)
 		goto err_clk_pwr;
@@ -70,7 +68,6 @@ nvkm_device_tegra_power_up(struct nvkm_device_tegra *tdev)
 err_clamp:
 	clk_disable_unprepare(tdev->clk_pwr);
 err_clk_pwr:
-	if (tdev->clk_ref)
 	clk_disable_unprepare(tdev->clk_ref);
 err_clk_ref:
 	clk_disable_unprepare(tdev->clk);
@@ -87,7 +84,6 @@ nvkm_device_tegra_power_down(struct nvkm_device_tegra *tdev)
 	int ret;
 
 	clk_disable_unprepare(tdev->clk_pwr);
-	if (tdev->clk_ref)
 	clk_disable_unprepare(tdev->clk_ref);
 	clk_disable_unprepare(tdev->clk);
 	udelay(10);