drm/exynos: remove unnecessary runtime pm operations

In booting, we can see a below message.

[    3.241728] exynos-mixer 14450000.mixer: Unbalanced pm_runtime_enable!

Already pm_runtime_enable is called by probe function. Remove
pm_runtime_enable/disable from mixer_bind and mixer_unbind.
Signed-off-by: NJoonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -1262,8 +1262,6 @@ static int mixer_bind(struct device *dev, struct device *manager, void *data)
 		return ret;
 	}
 
-	pm_runtime_enable(dev);
-
 	return 0;
 }
 
@@ -1272,8 +1270,6 @@ static void mixer_unbind(struct device *dev, struct device *master, void *data)
 	struct mixer_context *ctx = dev_get_drvdata(dev);
 
 	mixer_mgr_remove(&ctx->manager);
-
-	pm_runtime_disable(dev);
 }
 
 static const struct component_ops mixer_component_ops = {